WO2025192438A1 - Cover film - Google Patents

Abstract

The present invention addresses the problem of providing a cover film that generates few shavings when cut.　This cover film contains a cellulose acetate substrate and a polymer layer containing a polymer. The cross-section degree of orientation of the cellulose acetate substrate is no greater than 0.150.

Description

Cover film

The present invention relates to a cover film.

In the medical field of cytology and histology, a method for observing a microscopic specimen under a microscope is known. One method for preparing such a microscopic specimen involves automatically overlaying a cover film, which has a polymer (e.g., an adhesive or a compound that can act as an adhesive) on a support, onto a substrate (e.g., a glass slide) on which a few drops of a solvent capable of swelling and/or dissolving the polymer (hereinafter also referred to as "mounting liquid", e.g., xylene) has been dropped, and on which the specimen is placed, using an automatic mounting device to adhere (hereinafter also referred to as "mounting") the cover film to the substrate. This method allows for the preparation of a microscopic specimen in which the specimen is fixed between the substrate and the cover film.

For example, Patent Document 1 discloses an invention relating to a transparent film including a support film containing cellulose triacetate or a mixture of cellulose ester and cellulose triacetate as its main component.

US Patent Application Publication No. 2018/0194913

When using a cover film for encapsulation, the cover film is often cut before use. However, cutting the cover film can generate chips, and if these chips get mixed into the encapsulated sample, they may affect visibility during observation. Therefore, there is a need to further suppress the generation of chips when cutting the cover film.
The present inventors have studied the cover film with reference to Patent Document 1 and have found that there is room for further improvement in terms of the generation of chips during cutting.

The present invention aims to provide a cover film that produces less chips when cut.

As a result of extensive research into resolving the above-mentioned issues, the inventors have discovered that the following configuration can resolve the above-mentioned issues.

[1] A cover film comprising a cellulose acetate support and a polymer layer containing a polymer, wherein the cellulose acetate support has a degree of cross-sectional orientation of 0.150 or less.
[2] The cover film according to [1], wherein the glass transition temperature of the cellulose acetate support is 170 to 190°C.
[3] The cover film according to [1] or [2], wherein the breaking elongation of the cover film is 10% or more.
[4] The cover film according to any one of [1] to [3], wherein the polymer is a copolymer containing two or more repeating units derived from a monomer selected from the group consisting of acrylate, methacrylate, styrene, and acrylamide.
[5] The cover film according to any one of [1] to [3], wherein the polymer is a copolymer containing two or more repeating units derived from a monomer selected from the group consisting of ethyl acrylate, n-butyl acrylate, methyl acrylate, cyclohexyl acrylate, benzyl acrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, methyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, acetoacetoxyalkyl methacrylate, styrene, and dimethylacrylamide.
[6] The cover film according to any one of [1] to [5], which is used to cover an object to be examined on a substrate.

The present invention provides a cover film that produces less chips when cut.

The present invention will be described in detail below.
The following description of the components may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment.

In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the upper and lower limits. In the numerical ranges described in stages in this specification, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.
In this specification, a combination of two or more preferred aspects is a more preferred aspect.
In this specification, the amount of each component in a composition or layer means the total amount of the multiple substances present in the composition when multiple substances corresponding to each component are present in the composition, unless otherwise specified.

In this specification, "(meth)acrylic" is a general term for acrylic and methacrylic, and means "one or more of acrylic and methacrylic." Similarly, "(meth)acrylate" means "one or more of acrylate and methacrylate."
In this specification, unless otherwise specified, the refractive index refers to the refractive index for light with a wavelength of 550 nm measured using an Abbe refractometer (NAR-2T manufactured by Atago Co., Ltd.).

In this specification, unless otherwise specified, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are molecular weights determined by gel permeation chromatography (GPC) using columns of TSKgel GMHxL, TSKgel G4000HxL, TSKgel G2000HxL, and/or TSKgel Super HZM-N (all trade names manufactured by Tosoh Corporation), using THF (tetrahydrofuran) as the solvent, detecting with a differential refractometer, and converting the values using polystyrene as the standard.

In this specification, the term "step" includes not only an independent step, but also a step that achieves the intended purpose of the step even if it cannot be clearly distinguished from other steps.
In this specification, the term "conveyance direction" refers to the longitudinal direction of a film-like member or sheet-like member during production, and is synonymous with "longitudinal direction" and "MD (Machine Direction)."
In this specification, the term "width direction" refers to a direction perpendicular to the transport direction, and is synonymous with "TD (Transverse Direction)" and the like.
Furthermore, with regard to angles, "orthogonal" or "perpendicular" means a range of 90°±5°, and "parallel" means a range of 0°±5°. Similarly, with regard to angles, unless otherwise specified, it means that the difference from the strict angle is within 5 degrees. The difference in the above angles is preferably within 4 degrees, and more preferably within 3 degrees.
In this specification, a better effect of suppressing the generation of chips when cutting the cover film is also referred to as "a better effect of the present invention."

[Cover film]
The cover film of the present invention comprises a cellulose acetate support (hereinafter also referred to as an "AC support") and a polymer layer containing a polymer.
The configuration of the cover film of the present invention will be described in detail below.

<AC support>
The AC support included in the cover film of the present invention is a support containing cellulose acetate as a main component. "Containing cellulose acetate as a main component" means that cellulose acetate is the component contained in the largest amount among the components contained in the AC support.
The content of cellulose acetate is preferably more than 50% by mass, more preferably 80% by mass or more, based on the total mass of the AC support. The content of cellulose acetate may be 100% by mass or less, preferably 95% by mass or less, based on the total mass of the AC support.

(AC Support Material)
The AC support is not particularly limited, and any known AC support material containing cellulose acetate as a main component can be used.
Examples of cellulose acetate include cellulose-based polymers such as cellulose triacetate (TAC), cellulose diacetate, and cellulose monoacetate, with cellulose triacetate being preferred.
The degree of substitution of cellulose acetate is preferably from 2.00 to 3.00, more preferably from 2.40 to 2.95, and even more preferably from 2.85 to 2.95.
The degree of substitution can be measured by known methods such as FT-IR and titration.

The AC support may contain other components in addition to cellulose acetate.
Examples of the other components include at least one additive (hereinafter also referred to as "additive A") selected from the group consisting of sugars, polyesters, organic acids represented by general formula (1) described below, and compounds represented by general formula (2) described below.
The AC support preferably contains additive A, more preferably contains one or more selected from the group consisting of polyesters and compounds represented by general formula (2), and further preferably contains polyester.

-Sugars-
Examples of sugars include monosaccharides, disaccharides and polysaccharides, with disaccharides being preferred.
Monosaccharides include, for example, pentoses such as ribose, deoxyribose, arabinose and xylose, trioses, tetroses, hexoses, and heptoses.
Disaccharides include, for example, sucrose, lactose, maltose, trehalose, turanose and cellobiose, with sucrose being preferred.
Polysaccharides include, for example, glycogen and starch.
The saccharides may be either linear or cyclic. Examples of the cyclic saccharides include furanose rings and pyranose rings.

In some or all of the hydroxyl groups of the saccharide, the hydrogen atoms in the hydroxyl groups may be replaced with substituents. When hydroxyl groups in a plurality of hydroxyl groups are replaced with substituents, the plurality of substituents may be the same or different.
The substituent is preferably an acyl group, and the acyl group preferably has 1 to 10 carbon atoms.
Examples of the acyl group include aliphatic acyl groups such as a formyl group, an acetyl group, a propionyl group, a 2-methylpropionyl group, a 2,2-dimethylpropionyl group, and a 2-ethylhexanoyl group; and aromatic acyl groups such as a benzoyl group, a 1-naphthylcarbonyl group, a 2-naphthylcarbonyl group, and a 2-furylcarbonyl group.

-polyester-
As the polyester, known polyesters can be used, and polyesters containing a repeating unit represented by general formula (1A) and having capped ends are preferred.

In general formula (1A), X represents an acyclic divalent linking group having 2 to 10 carbon atoms. R represents an alkyl group having 1 to 8 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or an aryl group having 6 carbon atoms. m represents an integer from 0 to 4.

The term "non-cyclic" means that it does not contain a cyclic structure. Examples of groups that do not contain a cyclic structure include linear and branched groups.
Examples of the acyclic divalent linking group having 2 to 10 carbon atoms include alkylene groups having 2 to 10 carbon atoms, alkynylene groups having 2 to 10 carbon atoms, and the above alkylene groups and alkynylene groups having a heteroatom (for example, an oxygen atom, a nitrogen atom, etc.).
The non-cyclic divalent linking group represented by X preferably has 2 to 6 carbon atoms, and more preferably has 2 to 4 carbon atoms.
The acyclic divalent linking group represented by X may have a substituent. Examples of the substituent include an alkyl group, an alkoxy group, a hydroxyl group, a carboxyl group, and a group formed by combining these groups.

The group represented by R may have a substituent. Examples of the substituent include the substituents that X may have. Note that the number of carbon atoms in the group represented by R does not include the number of carbon atoms in the substituents that the group represented by R may have.
R may form a ring structure, such as a cyclohexyl group, a cyclooctyl group, a boronyl group, an isobornyl group, or a norbornyl group.
The alkyl group having 1 to 8 carbon atoms represented by R is preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group or an ethyl group.
Examples of the aryl group having 6 carbon atoms include a phenyl group and a 4-methylphenyl group.

m represents an integer of 0 to 4;
m is preferably an integer of 1 to 4, more preferably an integer of 1 or 2, and even more preferably 1 from the viewpoints of reactivity and availability of raw materials.

The terminally-capped polyester preferably has a terminal structure obtained by reacting the polyester terminal with a monoalcohol (or a monoalcohol derivative that can form an ester bond with the terminal carboxy group of the polyester) or a monocarboxylic acid (or a monocarboxylic acid derivative that can form an ester bond with the terminal hydroxyl group of the polyester). For example, when a polyester having a terminal carboxy group is obtained by reacting a dibasic acid with a diol, the polyester can be terminally capped with a monoalcohol residue by reacting it with a monoalcohol.
Furthermore, when a polyester having a terminal hydroxyl group is obtained, it can be reacted with a monocarboxylic acid to cap the terminal with a monocarboxylic acid residue. The residue is a partial structure of the polyester, and represents a partial structure that has characteristics of the monomers that form the polyester. For example, a monocarboxylic acid residue formed from a monocarboxylic acid R—COOH is R—CO—, and a monoalcohol residue formed from a monoalcohol R—OH is R—O—.
The polyester is preferably end-capped with an acyl group, and more preferably has a terminal structure obtained by reacting with a monocarboxylic acid.

Examples of polyesters include those described in paragraphs [0024] to [0035] of JP 2015-227955 A, the contents of which are incorporated herein by reference.

-Organic acid represented by general formula (1)-
The AC support may contain an organic acid represented by the following general formula (1).
X ¹¹ -L-(R ¹¹ ) _n (1)
^X11 represents an acidic group having an acid dissociation constant of 5.5 or less. L represents a single bond or a divalent or higher valent linking group. ^R11 represents an alkyl group having 6 to 30 carbon atoms, an alkenyl group having 6 to 30 carbon atoms, an alkynyl group having 6 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or a heterocyclic group having 6 to 30 ring members, and may further have a substituent. n is 1 when L is a single bond, and is (the valence of L - 1) when L is a divalent or higher valent linking group. In other words, L is a single bond or an (n+1) valent linking group.

The organic acid represented by the general formula (1) is preferably a partial derivative of a polyvalent organic acid. In this specification, the partial derivative of a polyvalent organic acid refers to a compound having a structure in which one molecule of a polyhydric alcohol is ester-bonded to one molecule of a fatty acid and a polyvalent organic acid, and having at least one unsubstituted acidic group derived from a polycarboxylic acid. In this specification, the term "fatty acid" refers to an aliphatic monocarboxylic acid. In other words, the fatty acid in this specification is not limited to so-called higher fatty acids, but also includes lower fatty acids having 12 or less carbon atoms, such as acetic acid and propionic acid.
The partial derivative of the polyvalent organic acid is preferably a partial derivative of a polyvalent carboxylic acid.
That is, the organic acid represented by the general formula (1) has a structure in which one molecule of a polyhydric alcohol is ester-bonded with one molecule of a fatty acid and one molecule of a polycarboxylic acid, and preferably has at least one unsubstituted carboxyl group derived from the polycarboxylic acid. The polycarboxylic acid used in the partial derivative of the polycarboxylic acid is not particularly limited, but is preferably, for example, succinic acid, citric acid, tartaric acid, diacetyltartaric acid, malic acid or adipic acid.

Examples of the polyhydric alcohols used in some of the derivatives of the polyhydric organic acids include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol, and glycerin, with glycerin being preferred. The organic acid represented by the general formula (1) above is preferably a so-called organic acid glyceride.

Examples of organic acids represented by general formula (1) include those described in paragraphs [0046] to [0049] of JP 2015-227955 A, the contents of which are incorporated herein by reference.

-Compound represented by general formula (2)-
The AC support may contain a compound represented by the following general formula (2).

In general formula (2), R ¹ , R ³ , and R ⁵ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, or an aromatic group. These alkyl groups, cycloalkyl groups, alkenyl groups, and aromatic groups may have a substituent. However, any one of R ¹ , R ³ , and R ⁵ is an alkyl group or cycloalkyl group substituted with a group having a ring structure, and the total number of ring structures present in R ¹ , R ³ , and R ⁵ is three or more.

The number of carbon atoms in the alkyl group in R ¹ , R ³ and R ⁵ is preferably 1 to 20, more preferably 1 to 10, still more preferably 1 to 5, and particularly preferably 1 to 3. The alkyl group is preferably a methyl group or an ethyl group.
However, in the case of an alkyl group substituted with a group having a ring structure, the number of carbon atoms therein is preferably 7 to 20, more preferably 7 to 12, and even more preferably 7 to 10. The ring structure in the alkyl group having a ring structure may be an aromatic ring (including an aromatic heterocycle) or an aliphatic ring, but is preferably an aromatic hydrocarbon group or an aliphatic ring.
The number of carbon atoms in the cycloalkyl group for R ¹ , R ³ , and R ⁵ is preferably 3 to 20, more preferably 3 to 10, still more preferably 4 to 8, and particularly preferably 5 or 6. Examples of the cycloalkyl group include a cyclopropyl group, a cyclopentyl group, and a cyclohexyl group, with a cyclohexyl group being preferred.
The number of carbon atoms in the alkenyl group in R ¹ , R ³ and R ⁵ is preferably 2 to 20, more preferably 2 to 10, and even more preferably 2 to 5. Examples of the alkenyl group include a vinyl group and an allyl group.
The aromatic groups in R ¹ , R ³ and R ⁵ may be aromatic hydrocarbon groups or aromatic heterocyclic groups, but are preferably aromatic hydrocarbon groups. The number of carbon atoms in the aromatic group is preferably 6 to 20, more preferably 6 to 16, and even more preferably 6 to 12. The aromatic group is preferably a phenyl group or a naphthyl group, and more preferably a phenyl group.

Each of the above groups R ¹ , R ³ and R ⁵ may have a substituent.
The substituent is not particularly limited and examples thereof include an alkyl group, an aryl group, an alkoxy group, an alkylthio group, an alkylsulfonyl group, a halogen atom, and an acyl group. An alkyl group, an aryl group, an alkoxy group, or an acyl group is preferred, and an alkyl group or an alkoxy group is more preferred.

It is preferable that any one of R ¹ , R ³ and R ⁵ is an alkyl group substituted with a group having a ring structure. The ring of the group having a ring structure is preferably a benzene ring, a naphthalene ring, a cyclopentane ring, a cyclohexane ring or a nitrogen-containing heteroaromatic ring (e.g., a pyrrole ring, a pyrazole ring, an imidazole ring, an oxazole ring, a thiazole ring, a pyridine ring, an indole ring, an isoindole ring, etc.).
In the compound represented by general formula (2), it is preferable that at least two of ^R1 , ^R3 , and ^R5 are alkyl or cycloalkyl groups having a ring structure as a substituent. Furthermore, it is preferable that ^R1 and ^R3 are each independently an alkyl group which may have a substituent, an aromatic group which may have a substituent, or a cycloalkyl group which may have a substituent.
In the compound represented by formula (2), it is more preferable that the total number of ring structures present in the substituents R ¹ , R ³ and R ⁵ is a maximum of four.

^R5 is preferably a group having a ring structure or an alkyl group or a cycloalkyl group which may be substituted with an acyl group, more preferably an alkyl group substituted with an aryl group, an alkyl group substituted with an acyl group (preferably an alkyl group substituted with an acyl group and an aryl group), or a cycloalkyl group, and still more preferably an alkyl group or cycloalkyl group substituted with an aryl group.

Among the compounds represented by formula (2), preferred compounds are listed below.
Compounds in which any one of ^R1 , ^R3 , and ^R5 is an alkyl group substituted with an aromatic ring. As the alkyl group substituted with an aromatic ring, one in which one or two aryl groups are substituted on the alkyl group (when two aryl groups are substituted, it is preferable that they are substituted on the same carbon atom). Furthermore, one in which an aryl group and an acyl group (preferably an aryloyl group) are substituted on the alkyl group is also preferred.
Compounds in which any one of R ¹ , R ³ and R ⁵ is a group containing a cycloalkyl group (preferably a cycloalkyl group).

In the compound represented by general formula (2), R ¹ , R ³ and R ⁵ are more preferably an alkyl group, an alkenyl group or an aryl group. Also, it is more preferable that R ¹ , R ³ and R ⁵ each have one or more ring structures, and even more preferable that each have one ring structure.

Specific examples of compounds represented by general formula (2) above are shown below.

The compound represented by general formula (2) and its synthesis method are also described, for example, in paragraphs [0072] to [0078] of JP 2015-227955 A, and these descriptions are incorporated herein by reference.

Additive A may be used alone or in combination of two or more.
The content of Additive A may be, for example, 30 parts by mass or less per 100 parts by mass of the cellulose acetate content in the AC support, and is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, in order to obtain better effects of the present invention. The lower limit is not particularly limited, and may be, for example, 1 part by mass or more, more preferably 3 parts by mass or more, per 100 parts by mass of the cellulose acetate content.

In addition to additive A, the AC support may contain known additives that are added to cellulose acylate films (e.g., ultraviolet inhibitors, anti-degradation agents, fine particles, optical property adjusters, etc.).

(Physical properties of AC support)
-Cross-sectional orientation-
The cross-sectional orientation degree P2z of the AC support contained in the cover film of the present invention is 0.150 or less.
The cover film of the present invention is characterized by including an AC support having a cross-sectional orientation degree P2z of 0.150 or less in addition to a polymer layer containing a polymer, thereby achieving the effect of suppressing the generation of chips when the cover film is cut.

The mechanism by which a cover film having an AC support cross-sectional orientation degree P2z of 0.150 or less is excellent in the effect of suppressing chips during cutting is not entirely clear, but the present inventors speculate as follows.
A cut surface is formed by cutting the cover film to a predetermined size for use in encapsulation. Here, when the cover film is cut, "shearing" occurs when a blade penetrates the film and separates it, and "fracture" occurs when the film is pulled and destroyed. As a result, the cut surface has a region of "shear surface" formed by shearing and a region of "fracture surface" formed by fracture. In conventional cover films, the region of the fracture surface formed by cutting tends to be relatively wide, but it is thought that this fracture surface is prone to generating chips because the shape of the cut surface is difficult to achieve.
In contrast, when the cross-sectional orientation degree P2z of the AC support contained in the cover film is 0.150 or less, when a blade is inserted into the cover film, it is less likely that the film will break due to tension, and the area of the fracture surface can be made narrower.As a result, the shape of the cut surface becomes more uniform, and it is presumed that the generation of chips can be suppressed.

The degree of cross-sectional orientation P2z of the AC support is defined as a value calculated from the results of X-ray diffraction measurement of the AC support by the following formulas (1) and (2).
(1) P=(3cos ² β-1)/2
(2) P2z=(Pxz+Pyz)/2
Here, Pxz in formula (2) is a value calculated from the measurement results of X-ray diffraction measurement performed on a cross section (xz plane) of the AC support including the x-axis, which is a direction in the plane of the AC support and is determined by a method described later, and the z-axis, which is a direction perpendicular to the main surface of the AC support, using the above formula (1). Similarly, Pyz in formula (2) is a value calculated from the measurement results of X-ray diffraction measurement performed on a cross section (yz plane) of the AC support including the y-axis, which is a direction in the plane of the AC support and is perpendicular to the x-axis, and the z-axis, using the above formula (1).
In formula (1), cos ² β is calculated from formula (3) below.
(3) cos ² β = ∫ (0, π) cos ² β I (β) sin β d β / ∫ (0, π) I (β) sin β d β
In formula (3), β is the angle between the plane of incidence of X-rays incident on the xz plane or yz plane and any one direction in the plane of the AC support, and I is the peak intensity of a peak present between 2θ of 7 and 11° in an X-ray diffraction chart obtained by measurement at angle β.

The X-ray diffraction measurement employs two-dimensional transmission X-ray measurement and is carried out using an X-ray diffraction device (for example, "RINT RAPID" manufactured by Rigaku Corporation) under the following conditions.
・X-ray source: Cu tube.
-X-rays are generated at 40kV-36mA.
・Collimator: 0.8mmφ.
The AC support sample is fixed to the transmission sample stage.
Exposure time: 600 seconds.

The x-axis and y-axis of the AC support for determining the above Pxz and Pyz are defined as follows by X-ray diffraction measurement of the AC support.
Using an X-ray diffractometer (for example, "RINT RAPID" manufactured by Rigaku Corporation) and an imaging plate reader (for example, "R-AXIS DS3C/3CL" manufactured by Rigaku Corporation), X-rays are incident on the AC support while rotating the AC support in its plane, and a diffraction photograph of the X-rays transmitted through the AC support is obtained. From the obtained diffraction photograph, an X-ray diffraction chart is obtained in all directions in the plane of the AC support. In the obtained X-ray diffraction chart, the direction in which the peak intensity present between 2θ of 7 and 11 degrees is the maximum is defined as the x-axis of the AC support. Furthermore, the direction perpendicular to the x-axis in the plane of the AC support is defined as the y-axis.

In terms of improving the measurement accuracy, it is preferable to perform humidity conditioning treatment on the AC support before measuring the degree of cross-sectional orientation P2z.
The humidity conditioning treatment is carried out, for example, by storing the AC support in an environment at a temperature of 25±5° C. and a relative humidity of 50±10% for 12 hours or more.

The cross-sectional orientation degree P2z of the AC support is preferably 0.130 or less, more preferably 0.115 or less, and even more preferably 0.110 or less, in terms of more excellent effects of the present invention. Although there is no particular restriction on the lower limit, it is preferably 0.050 or more, more preferably 0.080 or more, in terms of more excellent cutting processability.
The degree of cross-sectional orientation P2z of the AC support can be adjusted, for example, by changing the tension during film transport when producing the AC support, and the stretching conditions (stretching ratio, stretching speed, stretching temperature, etc.) From the viewpoint of suppressing the mobility of polymer chains, if stretching is performed under conditions of a slow stretching speed and/or a low stretching temperature, the degree of cross-sectional orientation tends to decrease.

- Glass transition temperature -
The glass transition temperature of the AC support is not particularly limited, but is preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, particularly preferably 175°C or higher, and is preferably 190°C or lower.
The glass transition temperature of the AC support can be obtained by heating the AC support layer obtained by peeling the polymer layer from the cover film from 25°C to 250°C at a rate of 10°C/min using a differential scanning calorimeter (DSC) and measuring the peak temperature of the observed peak.
The glass transition temperature of the AC support can be adjusted, for example, by the type of cellulose acetate and the type and content of additive A contained in the AC support, and the glass transition temperature tends to increase when the content of additive A is reduced.

-Thickness-
The thickness of the AC support is not particularly limited, but is preferably 50 to 250 μm, more preferably 50 to 150 μm, and even more preferably 100 to 150 μm.

- Refractive index -
The refractive index of the AC support is not particularly limited, but may be, for example, 1.440 to 1.600, and from the viewpoint of microscopic examination, it is preferably 1.460 to 1.560, which is close to that of a slide glass (refractive index 1.52 to 1.56).

The AC support is preferably transparent.
In this specification, "transparent" means that the transmittance of visible light (wavelength: 380 to 780 nm) is 60% or more. The transmittance is the ratio of transmitted light to incident light through the AC support. The transmittance of the AC support is preferably 80% or more, and more preferably 90% or more. There is no particular upper limit, and it may be 100% or less.
The transmittance is measured using a known measuring device in accordance with "Plastics - Determination of total light transmittance and total light reflectance" as defined in JIS K 7375:2008.

The AC support may be subjected to surface treatment such as ultraviolet irradiation, corona discharge, or glow discharge. A primer layer may also be provided on the surface of the AC support.

(Method for manufacturing AC support)
The AC support included in the cover film of the present invention can be produced by a known film-forming method such as solution film-forming or melt film-forming.
Examples of methods for producing an AC support include a production method having a film-forming step of forming a film from a composition containing cellulose acetate as a main component, and a stretching step of stretching the obtained film.
Each step will be described in detail below.

-Film forming process-
In the film-forming process, a film is formed using a composition containing cellulose acetate as a main component. Examples of film-forming methods include solution film-forming and melt film-forming, with the solution film-forming method being preferred. In the solution film-forming method, a film is formed using a solution (hereinafter also referred to as "dope") containing cellulose acetate, a solvent, and optional additives.

The solvent contained in the dope can be a known solvent used in preparing a solution casting dope. From the viewpoint of reducing the haze of the AC support, at least one solvent selected from the group consisting of ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms is preferred. The ethers, ketones, and esters may have a cyclic structure. Compounds having two or more functional groups selected from the group consisting of an ether bond (—O—), a ketone group (—CO—), and an ester bond (—COO—) can also be used as the solvent.
The solvent may have other functional groups such as alcoholic hydroxyl groups. In the case of a solvent having two or more types of functional groups, the number of carbon atoms may be within the range specified for a compound having any of the functional groups.
The dope may contain a poor solvent, such as methanol, ethanol, propanol, butanol, or water, with methanol being preferred.

The dope can be prepared by a known method, for example, by a method and apparatus for preparing a dope in a normal solvent casting method. The dope can be prepared by stirring cellulose acetate and a solvent at 0 to 40°C. A high-concentration dope may be stirred under pressure and heat. The heating temperature is usually 40°C or higher, preferably 60 to 200°C.
The components may be roughly mixed in advance and then placed in a container (tank, etc.), or may be added sequentially to the container.

The film-forming conditions and equipment are the same as those for the conventional production of cellulose acylate films, and the same solution casting film-forming conditions and equipment are used.
The prepared dope (cellulose acetate solution) is sent from a dope outlet to a pressure die, and is then uniformly cast from a nozzle (slit) of the pressure die onto the surface of an endless metal support (e.g., a metal drum, a metal band, or a metal belt). The resulting film is then peeled off from the endless metal support to obtain a film (hereinafter also referred to as a "web") mainly composed of cellulose acetate.

After casting the dope, the film may be pre-dried to remove at least a part of the solvent contained in the dope.
Pre-drying may be performed on either the film on the endless metal support or the film peeled off from the endless metal support. For example, pre-drying may be performed by clamping both ends in the width direction of the web peeled off from the endless metal support with tenter clips and transporting the web with a tenter.
Examples of methods for carrying out the preliminary drying include air drying in which air is blown onto the film (web) during transport, heat drying using a heating means such as a microwave or an oven, and a combination of these.

The casting and drying method in the solvent casting method is described in U.S. Pat. Nos. 2,336,310, 2,367,603, 2,492,078, 2,492,977, 2,492,978, 2,607,704, 2,739,069, and 2,739,070, British Patent Nos. 640,731, and 736,892, as well as Japanese Patent Publications 45-004,554, 49-005,614, JP-A 60-176,834, 60-203,430, and 62-115,035, the contents of which are incorporated herein by reference.
Further, as a film-forming method, cellulose acylate film-forming techniques described in JP-A Nos. 2000-301555, 2000-301558, JP-A Nos. 7-032391, 3-193316, 5-086212, 62-037113, 2-276607, 55-014201, 2-111511, and 2-208650 can be applied, and the contents of these film-forming techniques are incorporated herein by reference.

-Stretching process-
In the stretching step, the film (web) obtained in the film-forming step is stretched.
The direction of stretching in the stretching treatment may be either the conveyance direction or the width direction, or both, and it is preferable to stretch the web at least in the width direction.
When the web is stretched in the width direction, either uniaxial stretching in which the web is stretched only in the width direction or biaxial stretching in which the web is stretched in both the width direction and the conveying direction may be used, with biaxial stretching being preferred.
In the biaxial stretching treatment, stretching in the machine direction and stretching in the width direction may be carried out sequentially or simultaneously. When stretching in the machine direction and stretching in the width direction are carried out sequentially, the order is not particularly limited, but it is preferable to stretch the web in the machine direction and then stretch it in the width direction.
In this specification, for convenience, the term "stretching" also refers to a mode in which the web is transported by the method described below while maintaining the length in the transport direction or width direction, in other words, a mode in which the web is transported while the stretching ratio described below is kept at 0%.

The method for stretching the web in the width direction is not particularly limited, and known stretching methods can be applied, such as a method in which both widthwise ends of the web are fixed with clips or pins using a tenter apparatus and the distance between the clips or pins is increased in the width direction, and a method in which the distance is increased in both the width direction and the conveyance direction using a tenter apparatus, thereby simultaneously stretching the web in both directions.
As the stretching treatment in the width direction, stretching treatment by a so-called tenter method, in which stretching is performed using a tenter device, is preferred, because stretching treatment by the tenter method can perform smooth stretching treatment by driving the clip parts with a linear drive system, and the risk of breakage, etc. can be reduced.

The stretching ratio in the width direction stretching treatment is preferably 0 to 20%, more preferably 0 to 10%, in that this facilitates the production of an AC support having a cross-sectional orientation degree of 0.150 or less.
The stretching ratio (%) means a value calculated by the following formula.
Stretching ratio (%) = 100 × {(length after stretching) - (length before stretching)} / (length before stretching)

The stretching temperature in the width direction stretching treatment is preferably (Tg-5°C) to (Tg-50°C), more preferably (Tg-30°C) to (Tg-50°C), in that this makes it easier to produce an AC support having a cross-sectional orientation degree of 0.150 or less.
The stretching temperature (°C) is the temperature of the surface of the film (web) subjected to stretching treatment. Also, "Tg" means the glass transition temperature Tg (°C) of the AC support.

The stretching speed in the width direction stretching treatment is preferably 0 to 0.5%/sec, more preferably 0 to 0.3%/sec in the width direction, since this facilitates the production of an AC support having a cross-sectional orientation degree of 0.150 or less.
The stretching rate (%/sec) means a value calculated by the following formula:
Stretching rate (%/sec) = 100 × (length stretched per second during stretching) / (length before stretching)

There are no particular restrictions on the method for stretching the web in the conveying direction, and known stretching methods can be applied. Examples include a method in which the web is conveyed between multiple rolls with different rotation speeds and stretched in the conveying direction by utilizing the difference in rotation speeds; a method in which both ends of the web in the width direction are fixed with clips or pins using a tenter apparatus and the spacing between the clips or pins is increased in the conveying direction; and a method in which the spacing is increased in both the width direction and the conveying direction using a tenter apparatus, thereby simultaneously stretching in both directions.

When stretching in the machine direction is performed, the following stretching conditions are preferred.
The stretching ratio in the stretching treatment in the machine direction is preferably 0 to 20%, more preferably 0 to 10%.
The preferred range of the stretching temperature in the stretching treatment in the conveyance direction may be the same as the stretching temperature in the stretching treatment in the width direction, and is preferably (Tg-5°C) to (Tg-50°C), more preferably (Tg-30°C) to (Tg-50°C).
The stretching speed in the stretching treatment in the machine direction is preferably 0.1 to 0.5%/second, more preferably 0.1 to 0.3%/second in the machine direction.

The AC support included in the cover film of the present invention can be manufactured using the manufacturing method including the above-mentioned film-forming process and stretching process. However, the above-mentioned manufacturing method is merely one example, and the manufacturing method of the AC support is not limited to the above-mentioned manufacturing method, as long as an AC support having a cross-sectional orientation degree of 0.150 or less can be obtained.

<Polymer Layer>
The cover film has a polymer layer containing a polymer.

(polymer)
As the polymer, known polymers can be used.
Among these, polymers that dissolve or swell in organic solvents used as the filling liquid in automatic filling devices are preferred, and polymers that dissolve in the above organic solvents are more preferred.
Examples of organic solvents used as the sealing liquid in the automatic sealing device include a single solvent selected from the group consisting of toluene, xylene, mesitylene (1,3,5-trimethylbenzene), pseudocumene (1,2,4-trimethylbenzene), hemimellitene (1,2,3-trimethylbenzene), durene (1,2,4,5-tetramethylbenzene), ethyl acetate, methyl acetate, acetone, and methyl ethyl ketone, as well as a mixed solvent of two or more of these. The polymer swells in or dissolves in the organic solvent, thereby adhering the cover film and the substrate and sealing the analyte.

The polymer is preferably an acrylic resin, since it has excellent solubility in the above organic solvents.
In this specification, the acrylic resin means a polymer having repeating units derived from a (meth)acrylate monomer.
The acrylic resin is not particularly limited as long as it has a repeating unit derived from a (meth)acrylate monomer, and may be a homopolymer of one type of (meth)acrylate monomer or a copolymer of two or more types of (meth)acrylate monomers. The acrylic resin may also be a copolymer of one or more types of (meth)acrylate monomers and one or more types of monomers other than (meth)acrylate monomers (for example, an acrylamide monomer, a vinyl monomer, etc.).
In the acrylic resin, the content of repeating units derived from (meth)acrylate monomers is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, based on the total repeating units of the acrylic resin. The upper limit of the content of repeating units derived from (meth)acrylate monomers is not particularly limited, and may be 100% by mass based on the total repeating units of the acrylic resin.
It is particularly preferable that the acrylic resin contains only repeating units derived from (meth)acrylate monomers.
The acrylic resin can be prepared by a known method, for example, by polymerizing one or more (meth)acrylate monomers.

The (meth)acrylate monomer includes alkyl (meth)acrylate.
The alkyl group in the alkyl(meth)acrylate may further have a substituent. Examples of the substituent include an aryl group, and a phenyl group is preferred. The number of carbon atoms in the alkyl group in the alkyl(meth)acrylate that may have a substituent is preferably 1 to 15, more preferably 1 to 8, even more preferably 1 to 5, and particularly preferably 1 to 3.
Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, cyclohexyl (meth)acrylate, lauryl (meth)acrylate, benzyl (meth)acrylate, and acetoacetoxyalkyl (meth)acrylate.

Examples of the polymer include polymers containing at least one repeating unit derived from a monomer selected from the group consisting of alkyl acrylate, alkyl methacrylate, styrene, and acrylamide, and copolymers containing two or more repeating units derived from a monomer selected from the group consisting of alkyl acrylate, alkyl methacrylate, styrene, and acrylamide are preferred.
The alkyl acrylate and alkyl methacrylate have the same meanings as those already explained.

Specific examples of the above monomers include ethyl acrylate, n-butyl acrylate, methyl acrylate, cyclohexyl acrylate, benzyl acrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, methyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, styrene, lauryl methacrylate, lauryl acrylate, acetoacetoxyalkyl methacrylate, acetoacetoxyalkyl acrylate, dimethylacrylamide, and isopropylacrylamide.
Among these, the polymer preferably contains one or more repeating units derived from a monomer selected from the group consisting of ethyl acrylate, n-butyl acrylate, methyl acrylate, cyclohexyl acrylate, benzyl acrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, methyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, acetoacetoxyalkyl methacrylate, styrene, and dimethylacrylamide; more preferably contains one or more repeating units derived from a monomer selected from the group consisting of ethyl acrylate, methyl methacrylate, benzyl acrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, and cyclohexyl methacrylate; and even more preferably contains one or more repeating units derived from a monomer selected from the group consisting of ethyl acrylate and ethyl methacrylate.
Furthermore, copolymers containing two or more types of repeating units derived from monomers selected from any of the above groups are particularly preferred.

The weight average molecular weight (Mw) of the polymer is preferably 10,000 to 500,000, more preferably 50,000 to 140,000, and even more preferably 60,000 to 120,000.

The content of the polymer is not particularly limited, but is preferably 85% by mass or more, more preferably 90% by mass or more, relative to the total mass of the polymer layer. The upper limit may be 100% by mass or less.
The polymers may be used alone or in combination of two or more. When two or more polymers are used, they are preferably used in such a ratio that the mixed polymers do not cause turbidity in the dried film.

(Additives)
The polymer layer may contain additives different from the polymer.
Examples of additives contained in the polymer layer include carboxylic acid esters, phosphate esters, glycol compounds, deep eutectic solvents, and sulfonic acid esters.

Carboxylic acid esters are ester compounds produced by the reaction of a carboxyl group with a hydroxyl group. Examples of carboxylic acid esters include phthalic acid esters, trimellitic acid esters, pyromellitic acid esters, citrate esters, dipentaerythritol esters, carboxylic acid esters having an epoxy group, polyether esters, pentaerythritol esters, adipic acid esters, benzoic acid esters, adipate polyesters, and sebacate esters such as dioctyl sebacate.
Examples of phosphate esters include t-butylphenyl diphenyl phosphate, tricresyl phosphate, and isopropylphenyl diphenyl phosphate.
Examples of glycol compounds include polyethylene glycol, triethylene glycol bis(2-ethylhexanoate), and diethylene glycol dibenzoate.

Deep eutectic solvents (DES) are solvents containing a hydrogen bond acceptor compound and a hydrogen bond donor compound, and by mixing the hydrogen bond acceptor compound and the hydrogen bond donor compound, a eutectic melting point depression occurs, resulting in a significant decrease in the melting point of the solvent.
Examples of hydrogen bond acceptor compounds include quaternary ammonium compounds, phosphorus compounds, metal salts, amino acids, and polycarboxylic acids. Examples of hydrogen bond donor compounds include alcohol compounds, sugars, carboxylic acids, and amine compounds.
Examples of deep eutectic solvents include those described in U.S. Patent Application Publication No. 2018/0194913 and Japanese Patent Application Laid-Open No. 2020-105336, paragraphs [0025] to [0048].

Examples of additives contained in the polymer layer include the additives described in paragraphs [0036] to [0080] of JP-A-2015-227955.
The polymer layer may also contain a silane coupling agent, which will be described later.

The additives may be used alone or in combination of two or more.
When the polymer layer contains an additive, the content of the additive is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, based on the total mass of the polymer layer.
The upper limit of the content of the additive is not particularly limited, but from the viewpoint of adhesiveness of the polymer layer, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on the total mass of the polymer.

(Properties of polymer layer)
- Glass transition temperature -
The glass transition temperature of the polymer layer is preferably 50° C. or higher, more preferably 60° C. or higher, and even more preferably 65° C. or higher. The upper limit of the glass transition temperature of the polymer layer is, for example, 100° C., preferably 90° C. or lower, and more preferably 80° C. or lower.
The glass transition temperature of the polymer layer is determined by peeling the polymer layer from the cover film and measuring the peak temperature when the obtained polymer layer is heated from −50° C. to 100° C. at a rate of 10° C./min using a differential scanning calorimeter (DSC).
The glass transition temperature can be adjusted, for example, by changing the type and content of repeating units contained in the polymer.

-Thickness-
The thickness of the polymer layer is preferably from 1 to 100 μm, more preferably from 10 to 40 μm, and even more preferably from 10 to 30 μm.

- Refractive index -
From an optical viewpoint when observing with a microscope, the refractive index of the polymer layer is preferably 1.45 to 1.56, which is close to that of glass (refractive index 1.52 to 1.56), more preferably 1.46 to 1.56, and even more preferably 1.47 to 1.56.
In terms of ease of forming a polymer layer having the above-mentioned refractive index, it is preferable that the polymer constituting the polymer layer contains a repeating unit derived from one or more monomers selected from the group consisting of alkyl acrylate, alkyl methacrylate, and styrene. In terms of the above, the number of carbon atoms in the alkyl group in the alkyl acrylate or alkyl methacrylate is preferably 1 to 5, and more preferably 1 to 3.

<Other demographics>
The cover film may have layers other than the AC support and the polymer layer.
It is preferable that the cover film have a silane coupling agent layer on the surface opposite the AC support side of the polymer layer, in order to prevent blocking when the cover film of the present invention is stored in a rolled or stacked state and to improve storage stability over time.
The silane coupling agent layer may contain at least one selected from the group consisting of a silane coupling agent, a hydrolyzate thereof, and a hydrolysis condensate thereof (hereinafter, these are also collectively referred to as "silane coupling agents").

There are no particular restrictions on the type of silane coupling agent, but preferred are silane coupling agents that have two or more different reactive groups in the molecule, at least one of which chemically bonds with an inorganic material and at least one of which chemically bonds with an organic material.

Examples of silane coupling agents include vinyltrichlorosilane, vinyltris(β-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrimethoxysilane, γ-(methacryloxypropyl)trimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-chloropropyltrimethoxysilane.

The hydrolyzate of the silane coupling agent refers to a compound obtained by hydrolyzing the hydrolyzable group in the silane coupling agent.The hydrolyzate may be a compound in which all of the hydrolyzable groups are hydrolyzed (complete hydrolyzate), or a compound in which only a part of the hydrolyzable groups are hydrolyzed (partial hydrolyzate).In other words, the hydrolyzate may be a complete hydrolyzate, a partial hydrolyzate, or a mixture thereof.
In addition, the hydrolysis condensate of silane coupling agent refers to the compound obtained by hydrolyzing the hydrolyzable group in silane coupling agent and condensing the obtained hydrolyzate.It should be noted that the above-mentioned hydrolysis condensate may be the one in which all hydrolyzable groups are hydrolyzed and all the hydrolyzate is condensed (complete hydrolysis condensate), or the one in which some hydrolyzable groups are hydrolyzed and some of the hydrolyzate is condensed (partial hydrolysis condensate).In other words, the above-mentioned hydrolysis condensate may be the one in which all hydrolyzable groups are hydrolyzed and some of the hydrolyzate is condensed (partial hydrolysis condensate).

The silane coupling agents may be used alone or in combination of two or more.
The content of the silane coupling agent in the cover film is preferably 0.1 mg/m ² or more, more preferably 5 to 25 mg/m ² per unit area.

The other layer may be a backing layer.
The backing layer may be provided on the back surface of the AC support (the surface opposite to the surface on which the polymer layer is provided) for purposes such as preventing scratches on the surface of the cover film, more reliably preventing blocking during storage in a high-temperature environment, or improving the curling balance of the cover film.
Examples of materials that can be used to form the backing layer include synthetic polymers with high glass transition temperatures, such as polystyrene and polymethyl methacrylate, and gelatin.

<Cover film properties>
The total thickness of the polymer layer and the AC support in the cover film is preferably 250 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less, from the viewpoints of operability and microscopic examination during microscopic observation. The lower limit is preferably 50 μm or more, from the viewpoints of handling properties such as resistance to folding and encapsulation properties.

The breaking elongation of the cover film, measured by a tensile test using a tensile tester (for example, "Tensilon RTF-1310" manufactured by A&D Co., Ltd.), is preferably 5% or more, more preferably 10% or more, and even more preferably 14% or more, in terms of achieving better effects of the present invention. There is no particular upper limit, but it is preferably 30% or less, more preferably 25% or less, in terms of achieving better cutting processability.
The breaking elongation of the cover film is expressed as a percentage (%) and is calculated by the formula (( _L1 - _L0 )/ _{L0 )} x 100, where _L0 is the length of the cover film before the tensile test and L1 is the length of the cover film at break in the tensile test. The tensile test to measure the breaking elongation is carried out under conditions of 23°C and a relative humidity of 50%, at a pulling rate of 2 mm/min. A more specific method for carrying out the tensile test will be described in the examples below.
The breaking elongation of the cover film can be adjusted, for example, by the type of cellulose acetate contained in the AC support and the type and content of additive A, and the breaking elongation tends to increase when the content of additive A is reduced.

<Method of manufacturing cover film>
Examples of methods for providing a polymer layer on an AC support include coating with a coater or spray, casting, and transfer. Among these, it is preferred to form a polymer layer by coating a coating liquid prepared by dissolving a polymer in a solvent onto the AC support and then drying the coating film.

The type of solvent used in the coating solution is preferably one that can dissolve the polymer and has enough wettability to prevent repellency on the substrate, such as toluene, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, and xylene.
If a material capable of dissolving the surface of the substrate or a material capable of eluting low molecular weight components such as plasticizers contained in the AC support is used as the solvent for the coating solution, the polymer will penetrate into the surface layer of the AC support, increasing the adhesion between the polymer layer and the AC support, preventing peeling of the polymer layer and further suppressing the generation of chips during cutting.
From the above viewpoint, the coating liquid used to form the polymer layer preferably contains at least one of ethyl acetate and butyl acetate, and more preferably contains ethyl acetate.

After forming a coating film by applying a coating liquid containing the above polymer onto an AC support, it is preferable to carry out a drying step in which the obtained coating film is dried to remove the solvent from the coating film.
Drying treatments carried out in the drying step include a method in which the coating film is left at room temperature (23°C) for a predetermined time (e.g., natural drying), air drying in which gas is blown onto the coating film, and heat drying in which the coating film is heated using a heating means such as an oven, as well as combinations of these.

Examples of methods for forming the polymer layer and the silane coupling agent layer include a method in which a coating liquid prepared by dissolving a silane coupling agent in a solvent is applied to the surface of a coating film containing a polymer formed on an AC support, and the coating film is dried; and a method in which a coating liquid containing a polymer and a coating liquid prepared by dissolving a silane coupling agent in a solvent are simultaneously applied (multilayer coating) to the AC support, and the coating film is dried.
The solvent contained in the coating liquid is not particularly limited as long as it can dissolve the silane coupling agents, and examples thereof include the solvents listed above as solvents capable of dissolving the polymer.

<Application>
The cover film of the present invention can be suitably used as a cover film used to cover an analyte on a substrate. In particular, the cover film of the present invention is more preferably used for encapsulating an analyte, i.e., for bonding a substrate on which an analyte is placed and the cover film to fix the analyte between the substrate and the cover film. It is also more preferably used for preparing specimens for microscopic observation, and even more preferably for preparing specimens to be used in a microscope having an automatic encapsulation device.
The uses of the cover film of the present invention are not limited to the above uses, and can be used, for example, for sealing a thin film on a substrate, protecting an underlying layer by lamination, etc. The substrate to which the cover film is attached may be glass or a film-shaped material (such as a resin).

The present invention will be described in more detail below with reference to examples.
The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[Preparation of cover film]
The cover film in each example was prepared by applying a coating solution containing a polymer to an AC support. The detailed procedure is described below.

<Preparation of AC support>
(Preparation of Core Layer Cellulose Acetate Dope)
The following components were charged into a mixing tank and stirred to dissolve the components, thereby preparing a composition for a cellulose acetate dope for a core layer.

Cellulose acetate having an acetyl substitution degree of 2.88: 100 parts by mass.
Additives: In Examples 1 to 4 and Comparative Example 1, 10 parts by mass and 4 parts by mass of Additive A-1 and Additive A-2 were used, respectively. In Example 5, 10 parts by mass of Additive A-1 was used. In Example 6, 5 parts by mass of Additive A-1 was used. In Examples 7 and 8, 15 parts by mass and 4 parts by mass of Additive A-1 and Additive A-2 were used, respectively.
Methylene chloride: 430 parts by mass Methanol: 64 parts by mass

- Additives -
Additives A-1 and A-2 are additives (additive A) contained in each AC support.
Additive A-1: A polyester obtained by polycondensation of 1,2-cyclohexyldicarboxylic acid and ethylene glycol, having a terminal structure in which the hydrogen atoms of the hydroxyl groups at both ends are substituted with cyclohexanoyl groups (number average molecular weight: 913).
Additive A-2: A compound represented by the following formula (A-2) (a compound represented by general formula (2)).

(Preparation of outer layer cellulose acetate dope)
To 90 parts by weight of the above-mentioned cellulose acetate dope for the core layer, 10 parts by weight of a composition containing the following various components was added to prepare a composition for the cellulose acetate dope for the outer layer.

Silica particles (average particle size 20 nm, AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd.): 2 parts by mass; Methylene chloride: 76 parts by mass; Methanol: 11 parts by mass; Core layer cellulose acetate dope composition: 1 part by mass

(Preparation of AC support)
Each of the core layer cellulose acetate dope compositions and the outer layer cellulose acetate dope compositions was filtered through a filter paper with an average pore size of 34 μm, and then further filtered through a sintered metal filter with an average pore size of 10 μm. Next, using a band casting machine, the filtered core layer cellulose acetate dope composition and the filtered outer layer cellulose acetate dope compositions placed on both sides of it were simultaneously cast onto a drum at 20° C. from the casting nozzle.
Subsequently, the obtained film was peeled off from the band of the band casting machine, and both ends of the film in the width direction were fixed with tenter clips. While drying, the film was stretched under the stretching conditions (stretching temperature, stretching speed, and stretching ratio) described in the table below. In Examples 1 and 5 to 7, after the film was fixed with the tenter clips, the film was transported under the temperature environment described in the table below without changing the distance between the pair of tenter clips arranged in the width direction of the film.
Thereafter, the stretched film was further dried by passing it between rolls of a heat treatment device while being transported, to prepare an AC support (cellulose acetate film) having a thickness of 120 μm.

<Formation of polymer layer>
First, polymer A1 was synthesized according to the following procedure.
To a mixture of 38 parts by weight of toluene and 25 parts by weight of ethyl acetate, at 80 ° C. under a nitrogen atmosphere, a mixed solution of 90 parts by weight of ethyl acrylate (EA), 180 parts by weight of methyl methacrylate (MMA), 90 parts by weight of ethyl methacrylate (EMA), 98 parts by weight of toluene, 66 parts by weight of ethyl acetate, and 1.8 parts by weight of azoisobutyronitrile was added over 2 hours. Then, the resulting mixture was reacted for 2 hours while maintaining the temperature at 80 ° C. Then, 1.0 parts by weight of azoisobutyronitrile was added to the mixture, and the mixture was polymerized at 90 ° C. to a weight average molecular weight of 80,000 to obtain a solution containing polymer A1 (EA / MMA / EMA = 25 / 50 / 25 (mass ratio)).
To the obtained solution, 300 parts by mass of toluene and 487 parts by mass of ethyl acetate were added to obtain a coating solution 1.

Coating Solution 1 was applied to the surface of each AC support shown in the table using an extrusion coating method so that the final polymer layer would be 20 μm thick to form a coating film, and the resulting coating film was dried at 100°C for 5 minutes to form a polymer layer, thereby producing each of the cover films of Examples 1 to 8 and Comparative Example 1.

[measurement]
<Measurement of the degree of cross-sectional orientation P2z of AC support>
The AC support used to prepare each cover film was conditioned in an environment of 25° C. and a relative humidity of 60% for 24 hours.
Next, the x-axis and y-axis in the plane of the AC support were determined by the above-mentioned method using an X-ray diffractometer (RINT RAPID manufactured by Rigaku Corporation) and a general-purpose imaging plate reader (R-AXIS DS3C/3CL).
As a result of the measurement of the x-axis and y-axis, for each AC support, the x-axis was parallel to the transport direction in the manufacturing process of the AC support, and the y-axis was parallel to the width direction in the manufacturing process of the AC support.

X-ray diffraction measurements were performed under the above conditions on a cross section of each AC support including the direction perpendicular to the x-axis and out-of-plane direction (z-axis), and a cross section of each AC support including the direction perpendicular to the y-axis and out-of-plane direction (z-axis). The degree of cross-sectional orientation P2z of each AC support was calculated from the obtained measurement results using the above equations (1) and (2).

<Glass transition temperature (Tg) of AC support>
Each cover film was heated from 25°C to 250°C at a rate of 10°C/min using a differential scanning calorimeter, and the observed peak temperature was measured to determine the glass transition temperature Tg (°C) of the AC support.
When multiple peaks appeared in the DSC chart obtained by the above measurement, the glass transition temperature Tg of the substrate was obtained by distinguishing between peaks attributable to the substrate (100 to 250°C) and peaks attributable to the polymer layer (30 to 70°C) based on the temperatures at which the peaks appeared.

<Breaking elongation of cover film>
Each cover film was conditioned for 24 hours in an environment of 23°C and 50% relative humidity, and then punched using a punching cutter into a rectangular shape of 10 mm width and 50 mm length to prepare a sample for tensile testing.
A tensile test was performed using a tensile tester (Tensilon RTF-1310, manufactured by A&D Co., Ltd.) at a tension speed of 2 mm/min under an environment of 23°C and a relative humidity of 50%. The length of the sample at break was measured from the obtained stress-strain curve, and the breaking elongation was calculated from the length of the sample before and after the test. The tensile test was performed five times, and the arithmetic mean value of the values obtained in each test was taken as the breaking elongation (%) of the cover film.

[evaluation]
<Reducing chips during cutting>
Each cover film was cut and attached to a glass substrate using a Cover Aid automatic encapsulation device SCA-Film-J0 (manufactured by Sakura Seiki Co., Ltd.) to obtain an encapsulated sample. The size of the cover film and glass substrate of the encapsulated sample was 24 mm x 50 mm. The obtained encapsulated sample was visually inspected, and the number of observed chips was counted.
Thirty encapsulation samples were prepared, and the chip-prevention performance of the cover film when cut was evaluated based on the average value of the number of chips measured for each encapsulation sample, in accordance with the following criteria.

(Evaluation criteria for chip suppression)
A+: No chips observed in any of the encapsulated samples.
A-: The average number of chips confirmed in the enclosed sample was more than 0 and 3 or less.
B: The average number of chips confirmed in the enclosed sample was more than 3 and 10 or less.
C: The average number of chips confirmed in the enclosed sample was more than 10 and 30 or less.
D: The average number of chips found in the enclosed sample was more than 30.

[result]
The evaluation results are shown in Table 1. The descriptions in the table indicate the following.
In the table, the "Composition" column for "AC Support" shows the content of each of Additives A-1 and A-2 relative to 100 parts by mass of the cellulose acetate content in the AC support.
In addition, the "Cross-sectional orientation degree P2z" column in the "Film performance" section shows the cross-sectional orientation degree P2z of the AC support of the cover film of each example, the "Tg (°C)" column shows the glass transition temperature Tg (unit: °C) of the AC support of the cover film of each example, and the "Breaking elongation (%)" column shows the breaking elongation of the cover film of each example.

The results shown in the table confirm that the cover film of the present invention is excellent at suppressing the generation of chips during cutting. Furthermore, it was confirmed that the cover film of Comparative Example 1 was inferior in this effect because the cross-sectional orientation degree P2z of the support exceeded 0.150.

A comparison of Examples 3 and 4 confirmed that the effects of the present invention are superior when the cross-sectional orientation degree P2z of the AC support is 0.115 or less. Furthermore, a comparison of Examples 2 and 3 confirmed that the effects of the present invention are even superior when the cross-sectional orientation degree P2z of the AC support is 0.110 or less.

A comparison of Examples 1 and 7 confirmed that the effects of the present invention are superior when the glass transition temperature Tg of the AC support is 170°C or higher. Furthermore, a comparison of Examples 1, 5, and 6 confirmed that the effects of the present invention are even superior when the glass transition temperature Tg of the AC support is 175°C or higher.

A comparison of Examples 1 and 7 confirmed that the effects of the present invention are superior when the breaking elongation of the cover film is 10% or more. Furthermore, a comparison of Examples 1, 5, and 6 confirmed that the effects of the present invention are even superior when the breaking elongation of the cover film is 14% or more.

Claims (6)

a cellulose acetate support;
a polymer layer comprising a polymer;
A cover film, wherein the degree of cross-sectional orientation of the cellulose acetate support is 0.150 or less. The cover film according to claim 1, wherein the glass transition temperature of the cellulose acetate support is 170 to 190°C. The cover film according to claim 1, wherein the breaking elongation of the cover film is 10% or more. The cover film of claim 1, wherein the polymer is a copolymer containing two or more repeating units derived from monomers selected from the group consisting of acrylate, methacrylate, styrene, and acrylamide. The cover film of claim 1, wherein the polymer is a copolymer containing two or more repeating units derived from monomers selected from the group consisting of ethyl acrylate, n-butyl acrylate, methyl acrylate, cyclohexyl acrylate, benzyl acrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, methyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, acetoacetoxyalkyl methacrylate, styrene, and dimethylacrylamide. The cover film according to any one of claims 1 to 5, which is used to cover an object on a substrate.