JPH11123797A - Laminated sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sheet having an excellent surface gloss even in the case of thermoforming it by reducing a drawdown at the time of molding and incorporating mold adhesive properties for sufficiently closely adhering to a mold at the time of molding, and uniform moldability for making a molding thickness uniform after the molding in the case of a vacuum molding without accompanying with a pneumatic pressure. SOLUTION: The laminated sheet comprises a layer (A) made of a composition containing 100 pts.wt. of a propylene-α-olefin random copolymer including 80 to 90 mol.% of a homopoymer based on a propylene and 2 to 70 pts.wt. of a petroleum resin, and a layer (B) made of a propylene random copolymer containing 99 mol.% or more of a monomer unit based on a propylene homopolymer and/or propylene and laminated on the layer (A). The sheet also comprises a polypropylene sheet (C) and a laminated polypropylene film having 0.1 to 3.5 kgf/mm<2> of a tensile stress at 120 deg.C in a flowing direction of the film measured by a thermomechanical analysis under the condition of 100% of an elongation in tension and a direction perpendicular to the flowing direction of the film and laminated at least on one side surface of the sheet (C). In this case, the layer (B) becomes a front surface layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laminated sheet obtained by laminating a polypropylene film and a polypropylene sheet, which is suitable for thermoforming applications.

[0002]

2. Description of the Related Art Usually, food packaging containers such as lunch containers and food packs and general packaging containers are made of polyolefin sheets,
In particular, it is manufactured using a polypropylene sheet by a thermoforming method such as vacuum forming and pressure forming. In recent years, as environmental issues have become more important, the use of packaging containers made of these materials has been increasing.

[0003] In this thermoforming method, after heating a sheet or a film, the sheet or film is generally brought into close contact with a mold by an external force such as mechanical force, vacuum, or compressed air to form the sheet or film. At that time, a phenomenon (hereinafter, referred to as a drawdown) in which a central portion of a sheet or the like sags during heating before forming by a mold occurs. When heating is further continued, a force returns to a position before heating due to heat shrinkage of a central portion of the sheet or the like, and molding is performed when sagging most returns to the position before heating. Generally, the larger the drawdown, the more difficult it is to return to the position before heating, and therefore, the degree of the drawdown greatly affects the molding accuracy.

[0004] The forming accuracy depends not only on the drawdown described above but also on the tensile stress at the time of forming the heated sheet. That is, if the tensile stress at the time of molding is insufficient, a phenomenon called uneven thickness occurs in which the thickness of the molded product is not uniform when the mold is brought into close contact with the mold at the time of molding. On the other hand, if the tensile stress is excessive, there arises a problem that it is not possible to sufficiently adhere to the mold during molding, and a desired molded product shape cannot be obtained.

On the other hand, a non-stretched polypropylene film (hereinafter referred to as CPP) is applied to a polyolefin sheet, for example, a polypropylene sheet, for the purpose of imparting gloss to the packaging container or imparting a high-grade appearance to the packaging container by pre-printing.
(Referred to as film).

However, when a laminated sheet on which a CPP film is laminated is formed by a thermoforming method, a drawdown is large, and a phenomenon that the gloss is reduced at the time of molding also occurs, so that a molded product having high gloss can be obtained. could not.

[0007] Therefore, it has been proposed to use a biaxially oriented polypropylene film instead of the CPP film in the laminated sheet obtained by laminating the above CPP film. For example, JP-A-3-288641 discloses that a crystalline sheet has a smectic structure on a polypropylene sheet.
A laminated sheet having improved drawdown properties by laminating a biaxially oriented polypropylene film is disclosed.

However, in the laminated sheet disclosed in the above-mentioned publication, although the drawdown property can be improved, the tensile stress at the time of thermoforming becomes excessive, so that the sheet cannot be sufficiently adhered to the mold, and the molding accuracy is not improved. There was still room for improvement.

Against this background, the present inventors have proposed a laminated sheet formed by laminating laminated stretched polypropylene films having excellent molding accuracy and gloss (Japanese Patent Application No. 9-1034).
No. 45).

On the other hand, in the thermoforming method, the above-mentioned vacuum, compressed air,
There are various forming methods by combining external forces such as mechanical force, and examples thereof include vacuum forming, pressure forming, and vacuum forming. Above all, vacuum pressure forming in which both surfaces of a sheet or the like can be brought into close contact with a mold in a well-balanced manner is desirable from the viewpoint of molding accuracy. However, vacuum pressure forming requires a complicated and expensive forming machine to control both vacuum and pressure. Accordingly, there has been a demand for a sheet that can obtain a molded product with high molding accuracy even in vacuum molding that does not use pressurized air, which is a simpler and more general-purpose thermoforming method.

[0011] However, with the laminated sheet proposed by the present inventors, sufficient molding accuracy can be obtained in the above-mentioned vacuum press forming, but there is still room for improvement in the forming accuracy in vacuum forming without the use of pressurized air. Was.

[0012]

Therefore, not only the drawdown property can be improved, but also, especially in vacuum forming without the use of pressurized air, the mold adhesion and the thickness of the molded product after molding can be sufficiently adhered to the mold at the time of molding. There has been a demand for a sheet having both uniform moldability and uniform surface formability and excellent surface gloss even when thermoforming is performed.

[0013]

Means for Solving the Problems The present inventors have found that the above-mentioned lamination has good mold adhesion and uniform moldability, and also has good surface gloss after thermoforming, especially in vacuum molding without the use of compressed air. In order to develop the seat, we have been working diligently.

As a result, it has been found that the above-mentioned problems can be solved by a laminated sheet in which a polypropylene film having specific physical properties, film composition and layer constitution is laminated on a polypropylene sheet, and the present invention has been completed.

That is, the present invention relates to 100 parts by weight of a propylene-α-olefin random copolymer containing 80 to 98 mol% of a propylene-based monomer unit and 2 to 70 parts of a petroleum resin.
A layer (A) composed of a composition of a propylene homopolymer and / or a propylene-based monomer unit in an amount of 99 parts by weight.
A flow direction of the film and a flow direction of the film as measured by thermomechanical analysis under a condition of 100% tensile elongation, comprising a laminate with a layer (B) of a propylene-based random copolymer containing at least mol% Tensile stress at 120 ° C. in a direction perpendicular to the direction is 0.1 to 3.5 kgf
/ Mm ² , wherein the laminated polypropylene film is laminated on at least one surface of the polypropylene sheet (C), and the layer (B) is constituted as a surface layer.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the propylene-α-olefin random copolymer used as a raw material for the layer (A) of the laminated polypropylene film has a monomer unit content of 80 mol based on propylene. % Or more and 98 mol% or less. If the content of the monomer unit based on propylene is less than 80 mol%, the surface gloss of the laminated sheet after thermoforming is undesirably reduced. On the other hand, when the content of the monomer unit based on propylene is more than 98% by mole, the tensile strength at the time of heating of the laminated polypropylene film is increased, so that the die adhesion when thermoforming the laminated sheet is reduced. It is not preferable because it decreases. As the α-olefin monomer other than propylene in the propylene-α-olefin random copolymer, an α-olefin having 2 to 12 carbon atoms is preferable, and ethylene, 1-
Butene, 1-hexene, 4-methyl-1-pentene, 1
Α-olefins having 2 to 8 carbon atoms such as octene are more preferred. Specific examples of the propylene-α-olefin random copolymer used for the layer (A) include a propylene-ethylene random copolymer, a propylene-butene random copolymer, and a propylene-ethylene-butene random terpolymer. One or a mixture of two or more such as a coalesced copolymer and a propylene-hexene random copolymer can be exemplified.

The propylene-α-olefin random copolymer used as a raw material for the layer (A) has a peak-top measurement value of 125 to 150 ° C. in differential scanning calorimetry (hereinafter, referred to as DSC). Is preferred, and 130 to
The temperature is more preferably 147 ° C. When the measured value of the peak top in DSC is lower than 125 ° C., the surface gloss of the laminated sheet after thermoforming is undesirably reduced. The peak-top measured value in DSC is 150
If the temperature is higher than 0 ° C., the tensile stress at the time of heating of the entire laminated film becomes high, and the mold adhesion in the laminated sheet is undesirably reduced. Further, the melt flow rate of the propylene-α-olefin random copolymer (hereinafter referred to as MFR)
) Is preferably 1 to 15 g / 10 minutes in consideration of the hot tensile stress and the film formability.

In the present invention, the petroleum resin used as a raw material of the layer (A) of the laminated polypropylene film is not particularly limited, and specific examples thereof include an aliphatic hydrocarbon resin and an alicyclic hydrocarbon resin. , Rosin derivatives, terpene resins, terpene phenol resins and the like and hydrogenated resins thereof. Of these, hydrogenated hydrocarbon resins are particularly preferred because of their good transparency.

The softening point of the petroleum resin used as the raw material of the layer (A) is preferably from 60 to 160 ° C., and more preferably from 70 to 150 ° C. When the softening point is lower than 60 ° C, the operability is reduced due to adhesion between petroleum resins, and when the softening point is higher than 160 ° C, a propylene-α-olefin random copolymer in a melt extruder or the like. It is not preferable because it becomes difficult to blend them.

The melt viscosity of the petroleum resin used as the raw material for the layer (A) is 500 to 200,000 cps at 160 ° C.
And more preferably 700 to 150,000
More preferably, it is cps. If the melt viscosity at 160 ° C. is less than 500 cps, it is difficult to uniformly extrude the mixture with a melt extruder or the like, which is not preferable. Further, the melt viscosity at 160 ° C. is 200000c.
If it is larger than ps, propylene-α
-It is difficult to uniformly blend with the olefin random copolymer, which is not preferable.

The compounding amount of the petroleum resin in the raw material of the layer (A) needs to be 2 to 70 parts by weight based on 100 parts by weight of the propylene-α-olefin random copolymer.
More preferably, the amount is 3 to 60 parts by weight. If the blending amount of the petroleum resin is less than 2 parts by weight, it is not preferable because the mold adhesion in vacuum molding without using compressed air is reduced. When the blending amount of the petroleum resin is more than 70 parts by weight, the mold adhesion in vacuum forming without using compressed air is not further improved, and conversely, it is difficult to blend, and it is also difficult to extrude the composition. Is not preferred.

In the present invention, the method for producing the composition of the propylene-α-olefin random copolymer and the petroleum resin may be any known method without any limitation. A method in which a composition is formed by melt-kneading a petroleum resin and a method in which a propylene-α-olefin random copolymer and a petroleum resin are simply blended to form a composition. Among them, considering the blending properties and the extrusion characteristics of the composition, propylene-
A method in which an α-olefin random copolymer and a petroleum resin are melt-kneaded to form a composition is preferable.

In the present invention, the propylene random copolymer used as a raw material for the layer (B) of the laminated polypropylene film must have a propylene-based monomer unit content of at least 99 mol%. And 99.2
More preferably, it is at least mol%. If the content of the monomer unit based on propylene is less than 99 mol%, the surface gloss of the laminated sheet after thermoforming is undesirably reduced. In the propylene random copolymer, as the monomer other than propylene, a monomer copolymerizable with propylene can be used without any limitation, and among them, an α-olefin having 2 to 12 carbon atoms is preferable, Α having 2 to 8 carbon atoms such as ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene;
-Olefins are more preferred. Specific examples of the layer (B) raw material include propylene homopolymer, propylene-ethylene random copolymer, propylene-butene random copolymer, propylene-ethylene-butene random terpolymer, and propylene-hexene random. One type or a mixture of two or more types such as a copolymer can be exemplified.

The peak-top measured value of the propylene homopolymer and / or random propylene copolymer used for the raw material of the layer (B) is 150 to 165 ° C. in consideration of heat resistance. Preferably,
More preferably, the temperature is 155 to 165 ° C. The propylene homopolymer and / or the propylene-based random copolymer has a mmmm pentad fraction of preferably from 0.85 to 0.95 by ¹³ C-NMR, more preferably from 0.85 to 0.95.
More preferably, it is 6 to 0.94. When the mmmm pentad fraction is more than 0.95, the tensile stress at the time of heating of the film becomes high, and the mold adhesion is undesirably reduced. If the mmmm pentad fraction is less than 0.85, the surface gloss after thermoforming is undesirably reduced. The MFR of the propylene homopolymer and / or the propylene random copolymer is preferably from 1 to 15 g / 10 minutes, and more preferably from 2 to 15 g / 10 minutes, in consideration of hot tensile stress and film formability. Is more preferable.

In the raw material of the laminated polypropylene film used in the present invention, other resins can be mixed to such an extent that the physical properties of the film of the present invention are not impaired. The resin to be mixed is not particularly limited, but generally a homopolymer or a copolymer of propylene, ethylene, butene, or the like, or a mixture of two or more of these polymers can be used.

The raw material resin of the laminated polypropylene film may further contain, if necessary, an antistatic agent, an antifogging agent, an antiblocking agent, an antioxidant, a light stabilizer, a crystal nucleating agent, a lubricant, a slipperiness imparting agent and an antiblocking agent. Known additives such as a surfactant, a filler, and a foaming agent for the purpose of imparting properties may be mixed and used.

It is necessary that the laminated polypropylene film used in the present invention comprises a laminate of at least the layer (A) and the layer (B). That is, in the laminated polypropylene film, the layer (A) is necessary for improving the draw-down property and for imparting the mold adhesion in vacuum molding not particularly using air pressure.
Is necessary for imparting surface gloss and uniform moldability after thermoforming while improving drawdown properties. Further, the object of the present invention can be achieved only by laminating both layers. Further, in order to have the above-mentioned properties, the layer (A) is preferably sufficiently relaxed in orientation.
The layer (B) is preferably stretch-oriented.

In the case of a single-layer film comprising only the above-mentioned layer (A) or layer (B), even if the single-layer film satisfies the hot tensile stress specified in the present invention, the heat resistance of the present invention can be improved. It is not preferable because a laminated sheet having surface gloss even after molding and having sufficient uniform moldability and mold adhesion especially in vacuum molding without using pressurized air cannot be obtained. Contrary to the present invention, a laminated sheet laminated such that the layer (A) of the laminated polypropylene film becomes a surface layer is not preferred because the surface gloss after thermoforming is reduced.

Further, the laminated polypropylene film is
The structure is not limited to the two-layer structure of the layer (A) and the layer (B), and may be a three-layer structure of the layer (B), the layer (A), and the layer (B). It may be repeatedly laminated a plurality of times.

[0030] The thickness of the layer (A) of the laminated polypropylene film used in the present invention is determined to maintain the drawdown property,
Considering thermoforming properties such as mold adhesion, 5-100μ
m, more preferably 10 to 60 μm.

On the other hand, the thickness of the layer (B) of the laminated polypropylene film is preferably 0.5 to 50 μm, and more preferably 1 to 15 μm, in consideration of the surface gloss and the thermoformability such as uniform moldability. More preferably, there is.

The ratio of the thickness of the layer (B) to the total thickness of the laminated polypropylene film is 0.2 to 40.
%, More preferably 0.5 to 30%. When the ratio of the thickness of the layer (B) is less than 0.2%, the surface gloss is lowered, and when it is more than 40%, the thermoformability such as mold adhesion is lowered, which is not preferable.

The laminated polypropylene film used in the present invention is specified by thermomechanical analysis under specific conditions. That is, in thermomechanical analysis, 120 ° C. in a film flowing direction (hereinafter, referred to as MD direction) and a direction perpendicular to the flowing direction (hereinafter, referred to as TD direction).
Is required to be 0.1 to 3.5 kgf / mm ² under the condition of a tensile elongation of 100%, more preferably 0.2 to 3.5 kgf / mm ^2. 3.
It is 0 kgf / mm ² . Hot tensile stress is 0.1kgf
If it is less than / mm ² , the drawdown becomes large, and the uniform moldability also decreases, which is not preferable. If the hot tensile stress is greater than 3.5 kgf / mm ² ,
It is not preferable because the mold adhesion in vacuum molding without using compressed air is reduced.

The method for producing the laminated polypropylene film used in the present invention is not particularly limited, and a typical production method is a method in which the layer (A) and the layer (B) are laminated and then stretched. Is mentioned.

The method of laminating the layer (A) and the layer (B) is as follows.
In general, a method in which the layer (A) raw material and the layer (B) raw material are co-extruded and laminated, and the layer (A) and the layer (B) are further preferably employed.
Can be separately produced and laminated via a suitable adhesive, for example, an acid-modified polyolefin.

As the stretching method, in consideration of thermoformability and surface gloss after molding, a sequential biaxial stretching method or a simultaneous biaxial stretching method is suitably employed.

In the present invention, the stretching conditions in the above stretching method are not particularly limited, but the following laminated conditions can suitably obtain the laminated sheet aimed at by the present invention.

That is, the area stretching ratio is 1.5 to 35.
It is preferably 2 times, more preferably 2 times to 30 times, and still more preferably 4 times to 26 times. When the area stretch ratio is smaller than 1.5 times, the tensile stress at the time of heating of the laminated film is low, and thus the thermoformability such as uniform moldability is not preferable, and when the area stretch ratio is larger than 35 times, It is not preferable because the thermal tensile stress of the laminated film is increased and the thermoformability such as mold adhesion in vacuum molding without using compressed air is reduced.

The stretching ratio in the MD direction and the TD direction is preferably 1.5 to 8 times, more preferably 3 to 7 times, and the stretching ratio (a) in the MD direction and the TD direction. The ratio (a / b) of the stretching ratio (b) is
Considering thermoformability such as uniform moldability, 0.5 to 2 is preferable.

As the polypropylene sheet (C) having a laminated polypropylene film laminated on at least one surface used in the present invention, known polypropylene sheets (C) can be used without any limitation. As the raw material of the polypropylene sheet, propylene homopolymer, α-olefins other than propylene, for example, random, block of 20% by weight or less of ethylene, 1-butene, 1-pentene, etc. and 80% by weight or more of propylene, Graft copolymers, and further, mixtures thereof are mentioned.

Examples of the polypropylene sheet include stretched sheets such as a non-stretched sheet, a uniaxially stretched sheet, a biaxially stretched sheet, and a rolled sheet. Among them, an unstretched sheet is preferable in consideration of thermoformability.

The polypropylene sheet may be a foam sheet, a filler-containing sheet, or the like. As the filler compounded in the filler compound sheet described above,
Talc, mica, calcium carbonate, magnesium carbonate,
Known fillers such as silica and glass can be employed. The amount of these fillers is not particularly limited, but is preferably in the range of 5 to 50% by weight in consideration of the thermoformability of the laminated sheet.

The thickness of the polypropylene sheet is not particularly limited, but is 0.1 to 1 mm in consideration of thermoformability.
Is more preferable, and more preferably in the range of 0.2 to 0.6 mm.

The method of laminating the laminated polypropylene film and the polypropylene sheet used in the present invention is not particularly limited as long as the layer (B) of the laminated polypropylene film is laminated so as to be a surface layer. A known method such as a dry lamination method can be used.

Although the use of the laminated sheet of the present invention is not particularly limited, it can be suitably used for food packaging containers such as lunch containers and food packs, general packaging containers and the like. The molding method for these uses is not particularly limited, but a thermoforming method can be suitably used. Generally, vacuum forming, pressure forming,
A method such as vacuum pressurization or the like, followed by shaping in a mold such as a mold after heating, followed by cooling. Among them, vacuum forming without using compressed air is particularly preferable.

[0046]

EFFECT OF THE INVENTION The laminated sheet of the present invention has a small drawdown, in particular, mold adhesion that can sufficiently adhere to the mold during vacuum molding without using compressed air, and uniform molding in which the molded article thickness after molding is uniform. It is a sheet having both properties and excellent surface gloss even when subjected to thermoforming. Therefore, the laminated sheet of the present invention can be suitably used in the field of food packaging and general packaging.

[0047]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, which by no means limit the scope of the present invention. In the following Examples and Comparative Examples, the polypropylene resins used as film raw materials are those shown in Table 1.

[0048]

[Table 1]

The measuring methods used in the following Examples and Comparative Examples were implemented by the following methods.

(1) Pentad fraction (mmmm value) and copolymer composition Measured under the following conditions using JNM-GSX-270 ( ^13C- nuclear resonance frequency: 67.8 MHz) manufactured by JEOL Ltd.

Measurement mode: ¹ H-complete decoupling Pulse width: 7.0 microseconds (C45 degrees) Pulse repetition time: 3 seconds Integration frequency: 10,000 times Solvent: Mixed solvent of ortho-dichlorobenzene / deuterated benzene (90 / (10% by volume) Sample concentration: 120 mg / 2.5 ml Solvent Measurement temperature: 120 ° C. In this case, the mmmm pentad fraction was determined by measuring the splitting peak in the methyl group region of the ¹³ C-NMR spectrum. The assignment of the peak in the methyl group region is described in A.S.
Zambelli et al [Macromolec
ules 13, 267 (1980)].

(2) Tensile stress during heating Using a TMA / SS150C device manufactured by Seiko Electronic Industry Co., Ltd., a sample having a width of 2 mm is immersed in a heating medium set at 120 ° C., and the sample temperature becomes 120 ± 1 ° C. The measurement was started at that point. Tensile speed 5mm / min, distance between chucks 5
mm, tensile elongation 10 in MD and TD directions
The tensile stress at 0% was measured.

(3) Drawdown Property The laminated sheet was sandwiched between clamp frames (500 mm × 500 mm), the far-infrared heater was set at 300 ° C., and the laminated sheet was heated from above and below. The length from the position before heating at the center of the sheet to the lowest point of the sag was measured, and evaluated according to Table 2.

[0054]

[Table 2]

(4) Formability (Molding Accuracy) Tray (200 mm long, 250 mm wide, 20 mm high)
The height of 15 mm of the partition part (width 3 mm, height 15 mm) of the container when vacuum-forming without using air
%, The moldability was evaluated from the height of the partition part of the molded article under each condition. The evaluation was made in four stages as shown in Table 3.

[0056]

[Table 3]

(5) Transparency (haze) Measured according to JIS K6714.

(6) Surface Gloss (Gloss) Measured according to JIS K7105.

(7) Measurement of main peak by DSC After weighing about 5 to 6 mg of sample, the sample was sealed in an aluminum pan, and the temperature was raised from room temperature to 235 ° C. in a nitrogen flow of 20 ml / min with a differential calorimeter. Hold at this temperature for 10 minutes, then cool to room temperature at 10 ° C / min. Thereafter, the temperature of the main peak was measured by a melting curve obtained at a heating rate of 10 ° C./min.

(8) Softening point The softening point was measured according to JIS K2207 (ring and ball method).

(9) Melt viscosity Measured by a viscosity method (B-type viscometer).

Examples 1 to 4 The resins shown in Tables 1 and 4 were converted into 28
It was extruded into a sheet while being heated and melted at 0 ° C., cooled and solidified on a chill roll, then longitudinally stretched by a hot roll stretching machine, and subsequently stretched by a tenter transverse stretching machine. Area stretch ratio and M
Table 4 shows the stretching ratios in the D and TD directions. The obtained film was homo-polypropylene (MFR = 0.5 g / 10
Min, DSC peak temperature: 161 ° C.)
The sheet was laminated on a 5 mm sheet by using an extrusion laminating method, and was vacuum-formed without using air pressure. Thickness of the obtained film, haze, drawdown property of the obtained laminated sheet,
The moldability in vacuum molding and the surface gloss at the center of the molded product were measured. The results are shown in Table 4.

Comparative Examples 1 to 3 Film forming and molding evaluations were performed in exactly the same manner as in Example 1 except that the resins shown in Tables 1 and 4 were used, and the stretching ratio was changed as shown in Table 4. The results are shown in Table 4.

[0064]

[Table 4]

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Claims (1)

[Claims] 1. A propylene-based monomer unit comprising from 80 to 9
A layer (A) comprising a composition of 100 parts by weight of a propylene-α-olefin random copolymer containing 8 mol% and 2 to 70 parts by weight of a petroleum resin, and a propylene homopolymer and / or a propylene-based monomer unit The flow direction of the film, which is measured by thermomechanical analysis under the condition of a tensile elongation of 100%, comprising: a laminate with a layer (B) made of a propylene-based random copolymer containing 99% by mole or more of A laminated polypropylene film having a tensile stress at 120 ° C. in a direction perpendicular to the flow direction of the polypropylene sheet (C) of 0.1 to 3.5 kgf / mm ² is laminated on at least one surface of the polypropylene sheet (C), and the layer ( A laminated sheet, wherein B) is configured to be a surface layer.