JPH0416340B2 - - Google Patents

Description

Detailed Description of the Invention A: Technical Field of the Invention The present invention comprises a saponified ethylene-vinyl acetate copolymer layer with a specific composition and two specific types of adhesive layers, and has anti-blocking properties with a specific configuration. The present invention also relates to a composite film for thermal lamination that has excellent adhesive properties and no problems in slip properties and can be suitably put to practical use.

B. Prior Art and its Problems Conventionally used plasticized polyvinyl chloride films or sheets, generally referred to as flexible polyvinyl chloride, have an industrial content of about 25% by weight or more, often 30% by weight. Usually, a large amount of plasticizer is blended into the sheet, and although it is widely used to take advantage of its favorable properties, it suffers from the major drawback that the plasticizer migrates to the surface and oozes out. There is a need for a coating material that can cover the surface and eliminate the defects.

If a soft PVC sheet is used for a desk mat or document holder, for example, and it comes into contact with a document copied by an electrostatic copying machine, the printing ink will adhere to the soft PVC sheet in a very short time, causing the document to become damaged. There are problems in that the soft vinyl chloride sheet may be damaged or the soft vinyl chloride sheet may become contaminated, making it impossible to read characters, etc. on the printed surface through the sheet. Furthermore, furniture, office fixtures, etc. made from so-called PVC leather made of soft polyvinyl chloride, or covered with such leather, as well as wallpaper etc. made essentially of soft polyvinyl chloride, are also plasticized. There is a problem that must be solved in that it is easy to become contaminated due to migration and exudation of the agent onto the surface, and furthermore, this stain is difficult to wipe off. Furthermore, soft polyvinyl chloride films or sheets can be used as agricultural films or sheets for greenhouse horticulture such as crop cultivation greenhouses, tunnels, and mulch, compared to polyolefin films or sheets.
Although it is used suitably due to its advantages such as excellent heat retention, it has the disadvantage that when used for a relatively long period of time, the plasticizer migrates to the surface and oozes and becomes dirty, resulting in a decrease in light transmittance. There are similar technical issues. Although there have been many attempts to improve this drawback, no one has yet been found that achieves the objective and is satisfactorily put to practical use. The reality is that it is long awaited.

On the other hand, there have been attempts to eliminate this drawback by laminating other thermoplastic films on the flexible polyvinyl chloride film or sheet. The coating film used in practical use is an acrylic resin film that can be easily adhered to a film or sheet substantially made of soft polyvinyl chloride by thermal lamination to form a coating layer without using an adhesive. There is. However, the effect of preventing plasticizer migration and leaching is
Virtually not visible. Other thermoplastics can be thermally laminated without the use of adhesives, which are the easiest and most easily accepted by the PVC film or sheet manufacturers, and which are technologically the most simple and easily adopted. The coating cannot be applied by adhering to a flexible polyvinyl chloride film or sheet by a method. Under these circumstances, as with the acrylic resin, the coating can be immediately applied with good adhesive strength by thermal lamination without the need for the manufacturer to apply an adhesive. There is a strong need for a film for thermal lamination that can also prevent plasticizer from migrating to the surface and oozing out.

C Structure, purpose, and effect of the present invention The present inventors have investigated the plasticizer resistance, plasticizer resistance, migration, exudation properties of various thermoplastic films, and We have conducted extensive studies on the staining properties caused by external factors and the cleaning properties of such stains, and have developed a coating layer on at least one surface that has excellent stain resistance and does not migrate or seep onto the surface of the plasticizer. We have discovered a material that can be applied to plasticized polyvinyl chloride sheets or films by providing the following properties. Furthermore, a multi-layered adhesive that exhibits good adhesion to the material and a different adhesive from the above that exhibits good adhesion to plasticized polyvinyl chloride film, etc., is used, and the latter layer is provided with a specific thickness. By adopting a structure in which the adhesive layer is adjacent to the above-mentioned material, two types of composite films can be obtained that do not exhibit blocking properties, have no problems with slip properties, and can be thermally laminated. He discovered an adhesive and completed the present invention.

The present invention comprises a saponified ethylene-vinyl acetate copolymer layer A having an ethylene content of 20 to 60 mol% and a degree of saponification of the vinyl acetate component of 95% or more, a reactive polyurethane polymer layer B containing an isocyanate group, and a vinyl chloride component. and 40 to 90 mol% of vinyl acetate and/or (meth)acrylic acid ester component.
It is an object of the present invention to provide a composite film for thermal lamination having a vinyl chloride copolymer layer C containing ~1 mol % and having a composition of A/B/C.

D More detailed description of the present invention The saponified ethylene-vinyl acetate copolymer (hereinafter referred to as EVOH) used in the present invention has an ethylene content of 20 to 60 mol%, preferably 25 to 50 mol%.
The degree of saponification of the vinyl acetate component is 95% or more. Plasticizers for polyvinyl chloride include plasticizers that are liquid at room temperature, such as dibutyl phthalate, di-2-ethylhexyl phthalate, diisooctyl phthalate, diisodecyl phthalate, didecyl phthalate, dinonyl phthalate, and dilauryl, which have a melting point of 20°C or less. phthalate, phthalate plasticizers such as butyl lauryl phthalate, butyl benzyl phthalate, phosphate plasticizers such as tricresyl phosphate, tributyl phosphate, tri-2-ethylhexyl phosphate,
There are chlorine-containing plasticizers such as chlorinated paraffin, plasticizers that are solid at room temperature, such as dicyclohexyl phthalate, phthalate plasticizers such as phthalic acid diesters whose alcohol has 13 or more carbon atoms,
Examples include polyhydric alcohol plasticizers such as diventaerythritol fatty acid ester, and trimellitic acid plasticizers such as trioctyl trimellitate. Compared to these, EVOH with an ethylene content of 60 mol% or less and a saponification degree of 95% or more exhibits plasticizer resistance and plasticizer migration exudation resistance. Among these plasticizers, the former is a plasticizer that has particularly remarkable migration-exudation properties, but EVOH exhibits this effect, and in particular, EVOH with an ethylene content of 55 mol% or less, more preferably 50 mol% or less, is extremely plasticizer. having satisfactory properties,
Shows virtually no plasticizer permeability.

As the ethylene content increases, the plasticizer permeability gradually decreases, and when it exceeds 60 mol%, when laminated to a soft vinyl chloride sheet or film, the plasticizer gradually oozes out to the surface. As a result, stain resistance also decreases. On the other hand, as the ethylene content decreases, properties such as plasticizer permeability improve further, but in the region of less than 20 mol%, water resistance becomes poor, and it is used not only in agricultural films, but also in the document holder, wallpaper, etc. For example, when wiping off contamination caused by external factors unrelated to plasticizer exudation using a rag, the surface may swell or be damaged, so it is not suitable. More preferably, the ethylene content is 25 mol% or more. of the present invention
EVOH may have an ethylene content in the range of 20 to 60 mol%, more preferably 25 to 50 mol%, and may be a blend of two or more different ethylene contents within this range. EVOH with an ethylene content in the range of 20 to 60 mol% has practically satisfactory water resistance, but on the other hand, it is a hydrophilic polymer that can retain equilibrium moisture under the conditions of use, so it is susceptible to static electricity. It is suitable from this point of view as it can suppress the generation of dust and does not attract dust due to static electricity. From this point of view, the ethylene content is
More preferably, it is 50 mol% or less. Furthermore, as one of the more excellent embodiments that can improve plasticizer resistance, plasticizer migration and exudation resistance, and further improve the water resistance of the surface of the film, the EVOH film used in the present invention has a higher ethylene content. with EVOH layer and lower ethylene content.
A preferred embodiment is a composite structure consisting of an EVOH layer. That is, the composite EVOH film has an EVOH layer with an ethylene content of 20 to 35 mol% and an EVOH layer with an ethylene content of 40 to 60 mol%.
A more preferable embodiment is an embodiment in which the former layer, which has better plasticizer resistance and the like, is arranged adjacent to the adhesive layer. The two-layer EVOH film has two layers of different EVOH.
Two films may be laminated and used, but in particular, the two different types of EVOH may be co-extruded using a two-layer die, or the two types of EVOH in a molten state may be mixed inside the die or outside the die. A composite EVOH film obtained by integrating resin streams and having the above-mentioned different properties on the front and back sides is more preferably used. In this case, the two types
No adhesive resin is required between the EVOH layers, which is also more preferable.

EVOH has extremely good plasticizer resistance, so even if it is thin, it will still be effective.
When reaching extremely thin film thicknesses as shown below, damage such as scratches is more likely to occur, and on the other hand, with normal melting film forming operations, the technical difficulty increases when obtaining a film without pinholes, resulting in failure. This is not desirable as it increases the number of products. In addition, embossing is often applied due to the need for appearance, suppression of light selection, embossing of patterns, etc. In this case, the thickness of the EVOH layer is preferably at least 5μ or more. . Furthermore, if the EVOH layer exceeds 50μ, it is not only economically disadvantageous, but also affects the properties of the mating material to be heat laminated, such as impairing the flexibility of soft polyvinyl chloride sheets. So it's not desirable. More preferably, the thickness is 40μ or less.

The EVOH film may be in an unstretched and unheat-treated state, but it is more preferably heat-treated from the viewpoint of dimensional stability, water resistance, etc.
EVOH film has superior embossability compared to other resins, and the film for thermal lamination of the present invention is often suitably used after being laminated and then embossed. However, in such a case, the unstretched EVOH film
More suitable. Further, when higher water resistance is required, it is more preferable to use at least uniaxially stretched material. In this case, the stretching ratio is preferably 1.5 times or more in the case of uniaxial stretching, and an area stretching ratio of 3 times or more, more preferably 5 times or more in the case of biaxial stretching.

In order to obtain the composite film for thermal lamination of the present invention, the other most important requirement is a resin having thermal adhesive properties that is laminated on one side of the EVOH. The resin must exhibit good adhesion to EVOH and also to the substrate to be heat laminated, especially plasticized polyvinyl chloride, and the coated EVOH film must be resistant to blocking. After the composite film is obtained as a film for thermal lamination, it has a long shelf life at room temperature without deteriorating its performance as a film for thermal lamination. (the permissible period of neglect). The adhesive used in the present invention is two types of adhesives: a reactive polyurethane polymer B containing an isocyanate group and a vinyl chloride copolymer C containing 60 mol% or more of a vinyl chloride component. The layer is as above.
The EVOH layer A must have a thickness of at least 1 .mu.m and be used in a laminated form such that the configuration is A/B/C.

Here, as a vinyl chloride copolymer containing 60 mol% or more of vinyl chloride component,
More preferred are those containing 95 mol% and 30 to 5 mol% of vinyl acetate and/or (meth)acrylic acid ester components. Also vinyl acetate and/or
Alternatively, some (meth)acrylic acid ester components include a vinyl acetate component, a (meth)acrylic acid ester (mether ester, ether ester, etc.) component, or both of these components. Preferably, those containing It is also possible to use a vinyl chloride copolymer containing these components modified with an unsaturated organic acid such as maleic acid or itaconic acid or an anhydride thereof, or a third component such as (meth)acrylic acid. Among these, those modified with maleic anhydride are more preferred. A suitable content of these third components is 0.1 to 5 mol%. As a solvent for the copolymer, methyl ethyl ketone, ethyl acetate, butyl acetate, etc. are preferably used, and as a diluent, methyl ethyl ketone, toluene, etc. are preferably used. Reactive polyurethane polymers containing isocyanate groups are polymers that have two or more hydroxyl groups in the molecule, such as polyesters obtained by polycondensing ethylene glycol, propylene glycol, and adipic acid, or polyesters obtained by polycondensing ethylene glycol, propylene glycol, and adipic acid, or polyesters obtained by polycondensing ethylene glycol, propylene glycol, and adipic acid, and polyurethane polymers containing two or more hydroxyl groups in the molecule. A polymer having a hydroxyl group in the molecule obtained by partially saponifying a copolymer is mixed with a compound having two or more isocyanate groups in the molecule, for example, 1 mol of 1,6-hexamethylene glycol and 2 mol of 2 , 4-tolylene diisocyanate, or a reaction product of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate. Furthermore, a compound having two isocyanate groups in the molecule may be used alone. As the solvent for the polymer, ethyl acetate, butyl acetate, methyl ethyl ketone, toluene, xylene, etc., which have no reactivity with isocyanate groups, are preferably used.

When the adhesive C is used alone, that is, when the C side is in contact with the A side of a thermal lamination film having an A/C configuration, for example, when the film is wound up and stored until use, etc. C exhibits no blocking properties and has good slip properties, and also exhibits good thermal adhesion to sheets, films, paper, etc. made essentially of plasticized polyvinyl chloride, making it suitable. , C has a fatal flaw in that it has poor adhesion properties and is not sufficient for practical use. On the other hand, a film for thermal lamination consisting of A/B in which B is used alone has good adhesion between A and B as well as adhesion to sheets or films made essentially of plasticized polyvinyl chloride, paper, etc. However, when the A side is in contact with the B side, for example when the film is wound up and stored until use, it exhibits remarkable blocking properties.
It also has poor slip properties, which poses a major obstacle to its practical use.

Adhesives B and C are stacked on B so that the adhesive layer A has a composition of A/B/C, and the thickness of C is at least 1μ, preferably 1 to 10μ. When used, the film for thermal lamination of the present invention has excellent blocking resistance, no problems in slip property, and has a long shelf life. The thickness of C must be at least 1μ, and if the thickness of C layer is too small, B
It is presumed that this is due to the aforementioned unfavorable properties extending to C, but the details are not clear, but the blocking resistance and slip property of the composite film having the configuration A/B/C are satisfactory. It can't be. The thickness of B is not particularly limited, but if it is too thin, there will be problems such as difficulty in applying it uniformly over the entire surface, and if it is too thick, it will be economically disadvantageous, so it is 0.5 to 10μ. It is preferable, and 0.5 to several μ is appropriate.

A composite film with a composition of A/B/C, in which the two types of adhesives are used so that the thickness of C is at least 1 μm, has a long shelf life, and after long-term storage, plasticized polyvinyl chloride The thermal adhesion to films, sheets, paper, etc. is sufficiently satisfactory for practical use.

The multilayer adhesive layer can be provided on A by first coating B on one side of A, drying it, and then coating C on the B side. The coating is performed by any means known per se, such as gravure coating, row coating, doctor roll coating, doctor knife coating, bar coating, and curtain flow coating.

The composite coated film can be thermally laminated usually at a temperature of 120 to 160°C.
At lower temperatures, the adhesive force may not be developed sufficiently, and at higher temperatures, the condition of the EVOHA surface may deteriorate, which is not preferable.

The composite film for thermal lamination of the present invention is
As mentioned above, it is most preferably used as a film for thermal lamination to a plasticized polyvinyl chloride film or sheet, for example, a plasticized polyvinyl chloride film or sheet containing 25 to 55% by weight of the above-mentioned plasticizer based on the total weight. However, it also has good thermal adhesion to interior materials made essentially of paper, such as wallpaper, etc., and has excellent surface stain resistance as a covering material for such products made essentially of paper. It can be used suitably since it can provide excellent wiping properties of the stain and excellent embossing properties of the EVOH layer.

Next, examples will be described with reference to examples, but the scope of the present invention is not limited thereto.

Example 1 A 15μ thick film of EVOH with an ethylene content of 31 mol% and a saponification degree of vinyl acetate component of 99.3% was first coated with a gravure coater using a urethane adhesive AD335A and a curing agent Cat-10 (manufactured by Toyo Morton Co., Ltd., mixing ratio). 17:
1. Toluene/methyl ethyl ketone with a solid content concentration of 20% by weight (belonging to the above B) = 1/2 (weight ratio)
After drying at 110°C for ¹ minute, a maleic anhydride-modified vinyl chloride-vinyl acetate copolymer adhesive MPR-TM was applied on the coated surface. {Manufactured by Nissin Chemical Co., Ltd.
It belongs to the above C. Vinyl chloride (86 mol%) - Vinyl acetate (13 mol%) - Maleic anhydride (1 mol%)
Modified vinyl chloride-vinyl acetate copolymer. } was coated with a solution of toluene/methyl ethyl ketone = 1/2 (weight ratio) having a solid content concentration of 20% by weight at a coating weight of 2 g/m ² (based on solid content), and dried under the same conditions as above. The thicknesses of layer B and layer C of the obtained composite film were 2.1μ and 2.0μ, respectively. In order to examine the blocking properties of the obtained coated composite film, the uncoated EVOH film was brought into close contact with the C side of the coated composite film under a pressure of 50 g/cm ² and the adhesion after leaving for 24 hours was determined in practical terms. I checked to see if it would be a problem. No adhesion was observed, and it was confirmed that there was no problem with blocking properties. The coated composite film also had good slip properties. The coated composite film was coated with G-2 after 50 days.
- Contains 38% by weight of ethylhexyl phthalate
It was laminated onto the surface of a 0.3 mm soft polyvinyl chloride sheet by thermal lamination (using a roll at 150°C). The adhesive strength was measured by T-peeling, and it was confirmed that the soft polyvinyl chloride layer was destroyed and had sufficient adhesive strength. A soft polyvinyl chloride sheet laminated with the above composite film.
A non-plasticized soft polyvinyl chloride plate (6 cm x 6 cm, thickness 2 mm) was placed in close contact with the EVOH surface, and the amount of the plasticizer exuded and migrated was measured with a load of 2 kg applied to the hard vinyl chloride plate. The test was conducted at a temperature of 70°C. Even after 50 hours had elapsed, no increase in the weight of the hard polyvinyl chloride plate was observed, and no stickiness of the EVOH surface was observed, indicating that migration and oozing of the plasticizer was completely prevented. The surface remained undamaged even after wiping with a wet cloth, and showed sufficient water resistance. For comparison, AD335A and the above curing agent (mixing ratio)
17:1) or the above A/B using MPR-TM
Alternatively, a coated film having an A/C configuration was obtained according to the above method. The coated film having the structure A/B had significant blocking properties and poor slip properties, making it difficult to use as a film for thermal lamination. Although the coated film with the A/C configuration was satisfactory in terms of blocking and slipping properties, the adhesive strength between A and C was examined after laminating the soft polyvinyl chloride sheet, and the adhesive strength between A and C was 0.28 kg/ 25mm was insufficient for practical use.

For comparison, a sheet obtained by thermally laminating a film of an acrylic copolymer containing 86 mol% methyl methacrylate and 14 mol% butyl methacrylate and having the same thickness as the above EVOH onto the above flexible polyvinyl chloride sheet was prepared. It was also subjected to the same test. The weight change of the flexible polyvinyl chloride plate after 24 hours was 3.2% by weight. It was confirmed that the weight change was caused by the transfer of the plasticizer, and stickiness on the surface of the copolymer film was also observed.

Example 2 Except for Example 1, in which an EVOH film with an ethylene content of 43 mol% and a vinyl acetate component saponification degree of 99.3 mol% was used, the coated composite film was obtained and thermal lamination was performed at a temperature of 130°C. Exudation migration test of the plasticizer carried out according to Example 1,
A blocking property test was conducted. However, the coating amount of adhesive C was about 1.2 g/m ² , and as a result, the thickness of the C layer was 1.1 μm.

The coated composite film exhibited good anti-blocking properties and good slip properties. Further, no change in the weight of the hard polyvinyl chloride plate was observed. When the interlayer adhesive strength was measured by T-peel, the soft polyvinyl chloride layer was destroyed. The water resistance of the EVOH surface was also sufficient.

Example 3 EVOH (X) with an ethylene content of 26 mol% and a saponification degree of vinyl acetate component of 99.5 mol% and an ethylene content of 51
mol%, saponification degree of vinyl acetate component 99.3 mol%
EVOH (Y) is supplied to two extruders, and the molten resin is joined in the die at 220℃ using a two-layer T-die, so that the EVOH (X) layer has a thickness of 6μ,
A composite EVOH film with a (Y) layer thickness of 9 μm was obtained. The X side of the composite EVOH film is placed next to the soft polyvinyl chloride via a multilayer adhesive.
Thermal lamination was performed in accordance with Example 1, and various tests were conducted. However, the adhesives used were urethane adhesive EPS-703, curing agent KP-90 (manufactured by Dainippon Ink Co., Ltd., mixing ratio 15:1, belonging to B above), methyl ethyl ketone solution, and EPR- used in Example 1.
TM and the coating amount was 4g/m ² and 3g/m 2 , respectively.
As a result of setting g/ ^m2 , the thickness of each adhesive layer is B layer 3.9μ,
The composite film had a C layer of 3.1μ. In addition, for soft polyvinyl chloride sheets, Z-n is used as a plasticizer.
- Using a flexible polyvinyl chloride sheet containing 35% by weight of a mixture of octyl phthalate/tri-2-ethylhexyl phosphate = 50/50 (weight ratio) at 125°C.
Thermal lamination was carried out under the following temperature conditions.

The obtained coated composite film exhibited good blocking resistance and also had good slip properties. The flexible polyvinyl chloride sheet on which the composite film was laminated was examined in the same manner as in Example 1 to see if the plasticizer oozed out or migrated, and as a result, neither the weight change nor the surface stickiness was observed. The adhesive strength between the layers was also sufficient, and the polyvinyl chloride layer was broken when the adhesive strength was measured by T-peel.

For comparison, the acrylic copolymer film used in Example 1 was thermally laminated onto the flexible polyvinyl chloride sheet, and the resulting multilayer sheet was examined to see if the plasticizer oozed out or migrated. The weight increase of the hard PVC board is
After 30 hours, it was 3.1% by weight.

For comparison, we obtained a coated EVOH film consisting of A/B composition using EPS-703A as an adhesive, a curing agent, and KP-90, but the blocking property was
It had poor slip properties and could not be used as a film for thermal lamination.

Example 4 Using the biaxially stretched (area stretching ratio 3 x 3 times) EVOH film with an ethylene content of 49 mol% and a saponification degree of vinyl acetate component of 99.2% in Example 1,
Also, as a soft polyvinyl chloride sheet, plasticizer chlorinated paraffin/di-n-octyl phthalate =
The sheet containing 42% by weight of a 50/50 (weight ratio) mixture was mixed with AD-900 as a urethane adhesive and hardener AD-RT5 (manufactured by Toyo Morton Co., Ltd., mixing ratio 100:
15. Example 1 was carried out in the same manner as in Example 1, except for using the above-mentioned compound (belonging to B). The blocking resistance and slipping resistance of the coated composite film are both good, and the weight change of the hard vinyl chloride plate is also good.
No oozing to the EVOH surface was observed at all. The adhesion between the layers was also sufficient, and when the adhesion was measured by T-peel, the polyvinyl chloride layer was destroyed. Applicable
The water resistance of the EVOH surface was also sufficient.

In the case of a film made of the same acrylic copolymer as in Example 1 used for comparison, the weight change was 3.1% by weight, and stickiness on the surface of the film was also observed.

In addition, for comparison, a coated film consisting of A/B configuration using only urethane adhesive of AD-900 and curing agent AD-RT5 was obtained in the same manner as above. However, the blocking resistance and slipping resistance of the coated film were very unsatisfactory and could not be put to practical use.

Example 5 In Example 1, a mixture of tolylene diisocyanate (Coronate L, manufactured by Nippon Polyurethane Industries, Ltd.) and a glycol-terminated polyester having a molecular weight of approximately 800 (mixing ratio (weight)) was used as the urethane adhesive in Example 1.
The same procedure as in Example 1 was carried out except that 1:2) was used.
The coated composite film had good anti-blocking properties and good slip properties. Furthermore, no change in weight of the flexible polyvinyl chloride board was observed. The interlayer adhesive strength was sufficient, and the soft polyvinyl chloride layer was destroyed when the adhesive strength was measured by T-peel.

Example 6 Example 1 except that a copolymer containing 80 mol% of vinyl chloride component, 17 mol% of vinyl acetate component, and 3 mol% of ethyl acrylate component was used as the vinyl chloride adhesive C in Example 1. A film for thermal lamination obtained in the same manner as above exhibited good blocking resistance and good slip properties. The thermal lamination film was laminated on the surface of a soft vinyl chloride sheet in the same manner as in Example 1. Adhesive strength was measured by T-peel, and it was confirmed that the soft vinyl chloride layer was destroyed and had sufficient adhesion.

Claims (1)

[Scope of Claims] 1. A saponified ethylene-vinyl acetate copolymer layer A having an ethylene content of 20 to 60 mol% and a degree of saponification of the vinyl acetate component of 95% or more, a reactive polyurethane polymer layer B containing an isocyanate group, and 60 to 99 mol% vinyl chloride component and 40 to 1 mol% vinyl acetate and/or (meth)acrylic acid ester component
has a vinyl chloride copolymer layer C containing A/
A composite film for thermal lamination consisting of B/C composition. 2. The composite film according to claim 1, having an ethylene content of 25 to 50 mol%. 3. The composite film according to claim 1 or 2, wherein the thickness of A is 2 to 50 μm, the thickness of B is 0.5 to 10 μm, and the thickness of C is 1 to 10 μm. 4. Claim 1, wherein A consists of two layers: the saponified layer having an ethylene content of 20 to 35 mol% and the saponified layer having an ethylene content of 40 to 60 mol%, and the former is adjacent to B. The composite film according to any one of items 1 to 3. 5. The composite film according to any one of claims 1 to 4, which is used for thermal lamination to a film or sheet consisting essentially of plasticized polyvinyl chloride.