JP5141343B2 - Skin material for vehicle seats - Google Patents

Description

  The present invention relates to a skin material for a vehicle seat, and specifically to a leather skin material provided with a through hole.

As a method for forming a through hole in this type of leather (natural leather or artificial leather having a silver surface layer and a fiber layer), the techniques described in Patent Document 1 and Patent Document 2 are known. For example, in Patent Document 1, through holes are efficiently formed in leather by an automatically controlled punch mechanism (physical means).
The technique of Patent Document 2 is a technique for forming a through-hole in leather with a laser (optical means). By forming a through-hole while injecting a cooling medium onto the leather, the leather is burnt by the heat of the laser. Can be reduced as much as possible.

Then, after the leather that has been perforated in this way is used as a bag-like skin material, for example, a vehicle seat incorporating a member such as an acoustic device or a ventilation device is covered. Typically, after the bag-like skin material is turned upside down, the bag-like skin material is covered in a straight direction along the pad member of the rounded curved vehicle seat. At this time, as the position where the through hole is formed covers the member, by covering the vehicle seat with the skin material, the sound and wind of the member can be transmitted to the occupant side through the through hole provided in the skin material.
Japanese Patent Laid-Open No. 10-8100 JP 2001-138081 A

However, when a through-hole is formed in the skin material (leather), the surface rigidity of the formation portion is reduced. However, the above-described known technique has not been devised for reducing the surface rigidity. In particular, when a through hole is formed in a skin material of a vehicle seat, a countermeasure against this reduction in surface rigidity has been demanded.
Of course, it is possible to suppress a decrease in surface rigidity by forming a resin layer at the place where the through hole is formed (reinforcing with a resin layer). However, the flexibility of the skin material is partially reduced by the resin layer. . For this reason, if the skin material is covered along a rounded curved pad member, the portion where the resin layer is formed floats in a curved line at the curved portion, and the appearance is worse than expected.
The present invention has been made in view of the above points, and the problem to be solved by the present invention is to improve the appearance of a vehicle seat while preventing or reducing the decrease in surface rigidity of the skin material due to the formation of the through hole. It is to coat.

As means for solving the above problems, the skin material of the vehicle seat of the first invention is a skin material that covers a vehicle seat incorporating a member such as an acoustic device or a ventilation device, wherein the silver surface layer and the fiber It is the structure which covers the facing part of a member with the leather provided with a layer. The leather is provided with a through hole formed in at least a part of the facing portion and a resin layer covering the fiber layer, and the resin layer is reinforced to suppress a reduction in surface rigidity due to the formation of the through hole. ing.
Then, this skin material is put on the vehicle seat, and at this time, care should be taken not to deteriorate the appearance by the resin layer of the leather.

So, in this invention, the above-mentioned resin layer has the 1st site | part which faces a member, and the 2nd site | part formed around the 1st site | part. And the 2nd site | part is comprised by the resin amount less than a 1st site | part, and is set as the structure provided with the softness | flexibility which can deform | transform according to the external shape of a vehicle seat.
In this way, after the facing part of the member is covered with leather (first part of the resin layer), the leather part (second part of the flexible resin layer) around the member corresponds to the outer shape of the sheet (for example, It can be deformed (curved) and placed on the vehicle seat.

  A skin material for a vehicle seat according to a second invention is a skin material for a vehicle seat according to the first invention, wherein the resin layer is continuously or stepwise from the first part toward the second part. It is formed with regularity that reduces the amount of resin. For this reason, the skin material can be covered more naturally (for example, with a natural appearance and feel) corresponding to the outer shape of the vehicle seat.

  According to the skin material of the first invention of the present invention, it is possible to cover the vehicle seat with a good appearance while preventing or reducing the decrease in surface rigidity due to the formation of the through hole. And according to the skin material of 2nd invention, it can coat | cover on the vehicle seat more beautifully.

The best mode for carrying out the present invention will be described below with reference to FIGS. In FIG. 1, only one through hole is given a reference for convenience.
A vehicle seat 2 shown in FIG. 1 includes a seat cushion 4, a seat back 6, and a headrest 8, and these components are covered with a skin material (4S, 6S, 8S).
The seat back 6 has a rounded vertically long rectangular shape as a whole, and a pair of acoustic devices 9 and 9 are built in both shoulder openings. The both sides of the seat back 6 are slightly curved, and adjacent portions of the pair of acoustic devices 9 and 9 are curved toward the back of the seat (see FIG. 3). The acoustic device 9 includes cone paper 9a, a speaker body 9b, and a speaker grill 9c.

Further, referring to FIG. 1, the skin material 6 </ b> S is configured by sewing a plurality of pieces of natural leather in a bag shape, and a piece of natural leather that covers the acoustic device 9 (hereinafter referred to as natural leather 10). A plurality of through-holes 16 are formed. In this embodiment, the natural leather 10 is configured to suppress a reduction in surface rigidity associated with the formation of a through hole by reinforcing a resin layer (resin film 20, resin coating 40) described later.
Referring to FIG. 2, this natural leather 10 is a leather having an outer skin (silver surface layer 12) and a dermis (fiber layer 14), such as cow leather, horse leather, pig leather, deer leather, sheep leather, goat. Examples thereof include animal-based natural leather such as leather and kangaroo leather, and insect-based natural leather.

The skin material 6S (natural leather 10) is placed on the curved seat back 6 as will be described later. At this time, it should be considered that the appearance is not deteriorated by the resin layer of the natural leather 10.
Therefore, in each of the embodiments described later, while reducing the surface rigidity of the skin material 6S by the natural leather 10 manufactured by the “first step of covering the fiber layer with the resin layer” and the “second step of forming the through hole”, The seat back 6 is covered with a good appearance.

[Example 1]
(First step)
In the first step of the present embodiment, referring to FIG. 2, a thin resin film 20 (an example of a resin layer) is attached (coated) to the fiber layer 14 of the natural leather 10 with an adhesive 23. Integrate relatively firmly so as not to fray easily. In this embodiment, the resin film 20 is adhered to a portion facing a through-hole 16 described later and the periphery thereof (a part of the natural leather 10) (see FIG. 1).
The adhesive 23 is a resin that can bond the resin film 20 and the fiber layer 14, and examples thereof include urethane resins, acrylic resins, aminoplast resins, epoxy resins, glyoxal resins, and ethylene urea resins. For example, as the adhesive 23, it is preferable to use a urethane-based resin or an acrylic resin excellent in texture and durability.

(Resin film)
1 and 2, the resin film 20 includes a first portion 21 that faces the acoustic device 9 and a second portion 22 that is formed around the first portion 21.
The first portion 21 is formed at the central portion of the resin film 20 and is a portion where a through hole 16 described later is formed.
Moreover, the 2nd site | part 22 is provided with the some hole part 24, and is comprised by the resin amount small compared with the 1st site | part 21 of the plain state in which the hole part 24 is not formed. The hole 24 can be formed relatively easily by a laser irradiation device or a punch mechanism described later.

  In this embodiment, the plurality of hole portions 24 provided in the second part 22 continuously increase in diameter toward the periphery of the resin film 20 (from the first part 21 toward the second part 22). It is formed with regularity. That is, the second portion 22 is provided with a gradation due to the difference in diameter of the hole 24, and the second end 22 is deformed corresponding to the outer shape of the seat back 6 toward the peripheral end where the hole 24 having a larger diameter is formed. It is easy to do.

The resin film 20 is made of a resin (typically thermosetting resin) that can integrate the fiber layer 14. The resin film 20 is preferably composed of a stretchable resin, such as one or more resins selected from the group consisting of polypropylene (PP), polyethylene terephthalate (PET), and polyethylene (PE). Composed.
The thickness (rigidity) of the resin film 20 (first part 21) is set so that the surface rigidity of the part where the through hole 16 described later is formed and the surface rigidity of the part where the through hole 16 is not formed are as much as possible. It is desirable. For example, when the thickness dimension T1 of the natural leather 10 is 100, the thickness dimension T2 of the resin film 20 (first portion 21) is set to about 0.1 to 100 according to the number and the diameter dimension of the through holes 16. If it carries out like this, the surface rigidity and the elasticity which the natural leather 10 originally have can be provided to the resin film 20 (1st site | part 21 which formed the through-hole).

(Second step)
And in a 2nd process, with reference to FIG. 2, the natural leather 10 after a 1st process is mounted in a base (illustration omitted) by making the silver surface layer 12 into the front side. Then, a plurality of through holes 16 are formed in the natural leather 10 (the first portion 21 in the plain state) by irradiating a laser from the laser irradiation device 30 disposed above the natural leather 10. At this time, fraying of the fiber layer 14 is prevented or reduced by the resin film 20 in the through hole 16 formed in the natural leather 10, so that the cut surface becomes relatively sharp. In this embodiment, even if wrinkles caused by the burning of the fiber layer 14 adhere to the resin film 20, the wrinkles can be easily wiped by wiping the surface of the resin film 20.

(Coating work)
Then, the natural leather 10 that has been perforated is sewn together with other natural leather pieces in a bag shape and used as the skin material 6S of the seat back 6 (see FIG. 1).
Then, referring to FIG. 3, after covering the back surface of the skin material 6S with a cover pad 6CP that is more flexible than the pad member 6P, a cushion material 7 that improves sound insulation is provided on the facing portion with the acoustic device 9. Arrange and perform chamfering. The cushion material 7 is preferably a member that has air permeability and elasticity, has an effect of preventing sound attenuation, and holds the design surface shape of the seat back 6. For example, as the cushion material 7, a fiber entangled body (scouring body) formed by entanglement of a 3D net, a fiber mat, and a fiber material can be used.
And the skin material 6S is covered on the seat back 6 (pad member 6P) as a position arrangement | positioning where the formation place (cushion material 7) of the through-hole 16 covers the audio equipment 9. Specifically, the skin material 6S is put on the curved pad member 6P as a position arrangement where the formation portion (first portion 21) of the through hole 16 covers the acoustic device 9. At this time, the second portion 22 formed around the first portion 21 is disposed in the adjacent portion (curved portion) of the acoustic device 9.
Then, by deforming the second portion 22 in accordance with the curved shape of the pad member 6P, the skin material 6S can be covered more naturally (for example, with a natural appearance and feel) on the seat back 6. .

As described above, in this embodiment, the natural leather 10 (the second portion 22 for forming the hole 24) is configured with a smaller amount of resin than the first portion 21 so as to have flexibility that can be deformed into a curved shape. ing. For this reason, the skin material 6S can be coated with good appearance along the curved seat back 6.
The natural leather 10 (the first portion 21 for forming the through-hole 16) is given surface rigidity and stretchability that the natural leather 10 originally has. For this reason, according to the resin film 20, while the surface rigidity fall of the skin material 6S can be prevented or reduced, the seating performance of the seat back 6 becomes better.

Furthermore, the non-uniform fiber layer 14 (fluffy dermis) of the natural leather 10 is covered with a smooth resin film 20 (first portion 21), thereby suppressing the sound absorbing performance of the natural leather 10 that causes a decrease in sound quality as much as possible. be able to. Therefore, according to the present Example, the malfunction peculiar to natural leather can be improved and it can use suitably as the skin material 6S of the seat back 6. FIG.
In this embodiment, the resin film 20 is attached to a part of the natural leather 10 corresponding to the formation location of the through hole 16 (no extra resin layer is formed as much as possible). Work is simple. Further, in this embodiment, fraying of the through-hole 16 is suppressed as much as possible, so that it is possible to prevent or reduce the generation of odor due to scorching of the natural leather 10.

[Example 2]
Since each member and natural leather of the present embodiment have almost the same basic configuration as that of the first embodiment, common structures and the like are denoted by corresponding reference numerals, and detailed description thereof is omitted.
And the resin film 20 of a present Example has the 1st site | part 21 facing the acoustic apparatus 9, and the 2nd site | part 22 formed around the 1st site | part 21 with reference to FIG. The second portion 22 is provided with a plurality of notches 26 (triangular shape), and is configured with a smaller amount of resin than the plain first portion 21 where the notches 26 are not formed. .

  In this embodiment, the plurality of notches 26 (triangular) are formed with the periphery of the resin film 20 as the bottom, and toward the periphery of the resin film 20 (from the first portion 21 toward the second portion 22). And) having a regularity that continuously increases the notch area. That is, the second portion 22 is provided with a gradation due to a difference in the notch area, which is more flexible toward the peripheral end side where the notch area is larger, and is easily deformable in accordance with the outer shape of the seat back 6. . For this reason, the skin material 6 </ b> S of the present embodiment can be covered with a good appearance corresponding to the curved shape of the seat back 6 by the second portion 22 in which the notch portion 26 is formed.

[Example 3]
Since each member and natural leather of the present embodiment have almost the same basic configuration as that of the first embodiment, common structures and the like are denoted by corresponding reference numerals, and detailed description thereof is omitted.
In the first step, referring to FIG. 5, a resin composition (described later in detail) is applied to the fiber layer 14 of the natural leather 10 and covered with a resin coating 40 (another example of the resin layer). To do. In this resin coating 40, the fiber layer 14 of the natural leather 10 is covered, and some of the resin composition penetrates into the fiber layer 14 and hardens, so that the fiber layer 14 can be integrated more firmly. it can.

(Resin coating)
With reference to FIG. 5, the resin coating 40 has a first part 41 facing the acoustic device 9 and a second part 42 formed around the first part 41. The first portion 41 is formed at the central portion of the resin film 20 and is a portion where a through hole 16 described later is formed.
In addition, the second portion 42 is provided with a plurality of holes 24 and is configured with a smaller amount of resin than the plain first portion 41 where the holes 24 are not formed.
In this embodiment, the plurality of hole portions 24 provided in the second portion 42 continuously increase in diameter toward the periphery of the resin coating 40 (from the first portion 41 toward the second portion 42). It is formed with regularity. That is, the second portion 42 is provided with a gradation due to the difference in the diameter of the hole 24, and is more flexible toward the peripheral end side where the hole 24 having a larger diameter is formed. Correspondingly, the structure is easily deformable.

The resin coating 40 can be formed by applying the resin composition to the fiber layer 14 using a technique such as screen printing, spray coating, or impregnation by dipping.
Particularly in screen printing, the coating operation is extremely simple, and desired surface rigidity can be imparted to the natural leather 10 (first portion 41) relatively easily, and the hole 24 of the second portion 42 can be relatively formed. This is preferable because it can be easily formed. Further, in screen printing (typically computer control), for example, by controlling the thickness dimension of the resin coating 40 (first portion 41), the through-hole 16 forming portion (the resin coating 40 forming portion) and the through-hole are controlled. The surface rigidity and stretchability of the portion where 16 is not formed can be more easily equalized.

Here, the resin composition is a resin composition capable of forming a relatively smooth resin layer on the surface of the fiber layer 14 (dermis), and is an addition polymerization resin composition, an epoxy / urethane resin composition, and a condensation polymerization system. A resin composition can be illustrated.
More specifically, examples of the addition polymerization resin composition include acrylic resin (thermoplastic acrylic resin, thermosetting acrylic resin), vinyl resin, hydrocarbon resin, or rubber. Examples of the epoxy-urethane resin composition include epoxy resins (glycidyl ether-based, glycidyl ester-based, glycidyl amine-based), urethane resins (one-pack type, two-pack type), and polyurea resins. Moreover, a polyester resin, a melamine resin, a phenol resin, a polyamide resin, or a ketone resin can be illustrated as a condensation polymerization type resin composition. One or more resins selected from the group consisting of these resins or derivatives thereof may be used as the resin composition.

In the second step, the natural leather 10 after the first step is placed on the base 54. A punch member 50 (cylindrical shape) having a cutting edge at the tip is disposed above the base 54, and the punch member 50 can be moved up and down toward a concave portion 52 provided in the base 54 to support a support portion. (Not shown).
Then, the punch member 50 is lowered toward the natural leather 10 placed on the base 54 to form the through hole 16 in the natural leather 10. At this time, since the fiber layer 14 is more firmly integrated with the natural leather 10 by the resin coating 40, the silver surface layer 12 and the fiber layer 14 can be punched cleanly by the punch member 50. For this reason, fraying of the fiber layer 14 around the through hole 16 is more reliably prevented or reduced, and the cut surface of the through hole 16 becomes sharper.

Thus, in the present embodiment, the second portion 42 of the natural leather 10 is configured with a smaller amount of resin than the first portion 41 so as to have flexibility that can be deformed into a curved shape. For this reason, the skin material 6S can be coated with good appearance along the curved seat back 6.
According to the present embodiment, the fiber layer 14 of the natural leather 10 is covered with the stronger resin coating 40 (first portion 41), thereby further reliably preventing or reducing the decrease in the surface rigidity of the natural leather 10. be able to.
Furthermore, the non-uniform fiber layer 14 (fuzzy dermis) of the natural leather 10 is covered with a smoother resin coating 40 (first portion 41), thereby suppressing the sound absorbing performance of the natural leather 10 that causes a decrease in sound quality. be able to.

The skin material (leather) of this embodiment is not limited to the above-described examples, and can take other various embodiments.
(1) In this example, the resin film 20 (resin coating 40) is provided with holes 24 and notches 26 to reduce the amount of resin in the second portion 22 (42) (reducing the area of the resin layer) The configuration in which the amount of resin is reduced by doing so has been described.
Unlike this, the configuration in which the thickness of the second portion 22 is made smaller (thinner) than the first portion 21 to reduce the amount of resin continuously or stepwise (by reducing the thickness of the resin layer) It is good also as a structure which reduces quantity. In this case, it is preferable to continuously reduce the thickness of the resin layer (provide gradation) from the first part 21 toward the second part 22.

(2) In the present embodiment, an example (reasonable example) in which the second part 22 is provided around the entire circumference of the first part 21 has been described. Unlike this, a simple configuration may be adopted in which the second portion 22 is provided only in a portion (a part of the first portion 21) corresponding to the adjacent portion of the acoustic device 9.
(3) In this embodiment, the example in which the diameter of the hole 24 is continuously reduced has been described. However, the resin amount may be reduced by changing the diameter of the hole 24 stepwise.
Moreover, it is good also as a structure which makes the hole 24 the same and reduces the resin amount of the 2nd site | part 22 extremely with respect to the 1st site | part 21. FIG. The shape of the hole 24 may be a circular shape shown in the above embodiments, a substantially circular shape such as an ellipse, or a polygonal shape such as a rhombus, a triangle, a quadrangle, a pentagon, or a star.
(4) In Example 2, although the example which provides the notch part 26 in the resin film 20 was demonstrated, you may provide the notch part 26 in the resin coating 40. FIG. In addition to the triangular shape shown in each of the above embodiments, the shape of the notched portion is, for example, a shape in which the notch area continuously increases, such as a semicircular shape, a semi-elliptical shape, and an R-shaped triangular shape, It is good also as a shape where notch areas, such as a shape and square shape, become large in steps.

(5) Moreover, in Example 1, the example which forms the through-hole 16 in the natural leather 10 coat | covered with the resin film 20 with the laser irradiation apparatus 30 was demonstrated. Unlike this, the through hole 16 may be formed in the natural leather 10 covered with the resin film 20 by a punch mechanism. The first part may have a structure in which one through-hole 16 is formed, or a plurality of holes may be formed.
(6) Moreover, in Example 3, the example which forms the through-hole 16 in the natural leather 10 coat | covered with the resin coating 40 with the punch mechanism was demonstrated. Alternatively, the through-hole 16 may be formed in the natural leather 10 covered with the resin coating 40 by the laser irradiation device 30. The natural leather 10 covered with the resin coating 40 has a fiber layer 14 that is more firmly integrated, so that there is almost no odor due to scorching of the fiber layer 14.

(7) In the present embodiment, the structure of the skin material has been described using the natural leather 10 as an example. The method of the present embodiment can be applied to any leather provided with at least a fiber layer 14, and can be applied to, for example, artificial leather (a leather in which a silver surface layer and a fiber layer are made of resin).
In the present embodiment, an example in which a plurality of pieces of natural leather 10 are sewn in a bag shape to constitute the skin material 6S (an example in which all the skin material 6S is constituted by natural leather) has been described. Unlike this, the part facing the through-hole 16 and the periphery thereof (part of the natural leather 10) are made of natural leather 10, and the other part is made of another material (for example, woven fabric or artificial leather). Also good.
(8) In the present embodiment, the example in which the portion facing the through-hole 16 and the periphery thereof (a part of the natural leather 10) are covered with the resin layer has been described. However, all the natural leather constituting the skin material 6S is made of resin. It is good also as a structure coat | covered with a layer. In this case, the part excluding the part facing the through hole 16 is configured as the second part.
(9) If a deodorant such as activated carbon or titanium is mixed in the resin coating 40 or the adhesive 23 of this embodiment, the odor of the natural leather 10 can be removed more reliably.

(10) In the present embodiment, the vehicle seat 2 that exclusively incorporates the acoustic device 9 has been described as an example. The technique of the present embodiment is a technique applicable to various members covered with leather. In particular, it can be suitably used for various members (vehicle interior members such as vehicle seats and door trims) incorporating a ventilation device, a light source, or an acoustic device. The technique of this embodiment can also be applied to the case where decorative characters are created by the through holes 16 on the leather surface.
In the present embodiment, the seat back 6 (skin material 6S) has been described as an example of forming the through hole 16. However, the through hole 16 is formed in the seat cushion 4 (skin material 4S) and the headrest 8 (skin material 8S). In this case, the present embodiment can be preferably used.

(11) In the present embodiment, the example in which the through-hole 16 is formed with a laser or the like from the silver surface layer 12 side of the natural leather 10 has been described. Unlike this, the through hole 16 may be formed by laser or the like from the fiber layer 14 side of the natural leather 10. In this case, since the resin layer portion (partially) formed on the fiber layer 14 can be seen at a glance, the formation position of the through hole 16 can be easily positioned.
(12) In this embodiment, the example in which the through hole 16 is formed exclusively in one piece of leather has been described. Unlike this, the through-holes 16 can be simultaneously formed in a state in which a plurality of leathers are stacked. In this case, since the resin layer is interposed between the leather and the leather, the stacked stability is improved. For this reason, even if the punch member 50 is inserted, for example, the leather is less likely to be twisted, and the clean through-hole 16 can be formed.
Further, if the stacked leathers are separated by a resin layer (thermosetting resin), the leathers are not bonded to each other by the heat of the laser. For this reason, after the through holes 16 are formed, the stacked leathers can be separated cleanly one by one (sorting work becomes easy).

(13) In this embodiment, resin films (first resin film and second resin film) may be bonded to both surfaces of the silver surface layer 12 and the fiber layer 14 of the natural leather 10.
The adhesive strength of the first resin film on the silver layer 12 side is made weaker than the adhesive strength of the second resin film on the fiber layer 14 side (typically about 3.0 N / cm to 6.0 N / cm). The structure is easy to peel off. For example, it is preferable to set the adhesive strength of the first resin film to about 0.15 N / cm to 0.5 N / cm. By doing this, the first resin film is easily peeled without damaging the silver surface layer 12. be able to.
Thus, by covering both surfaces of the natural leather 10 with the first resin film and the second resin film, fraying of the fiber layer 14 and the silver surface layer 12 due to the heat of the laser can be prevented or reduced more reliably. Moreover, even if scorching or wrinkles adhere to the first resin film on the silver surface layer 12 side, the first resin film can be reliably wiped off by peeling the first resin film from the silver surface layer 12.

It is a partial perspective view of a vehicle seat. (A) It is a longitudinal cross-sectional view of the leather which formed the resin layer, (b) It is a longitudinal cross-sectional view of the leather which formed the through-hole, (c) It is a longitudinal cross-sectional view of the leather deform | transformed into the curved shape. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. FIG. 6 is a perspective view of a part of a vehicle seat according to a second embodiment. It is a longitudinal cross-sectional view of the leather which concerns on Example 3 which formed the through-hole.

Explanation of symbols

2 Vehicle seat 6 Seat back 6P Pad member 6S Skin material 9 Acoustic device 10 Natural leather 12 Silver surface layer 14 Fiber layer 16 Through hole 20 Resin film 21 First part 22 Second part 23 Adhesive 24 Hole part 26 Notch 30 Laser Irradiation Device 40 Resin Coating 41 First Part 42 Second Part 50 Punch Member 52 Recess 54 Base

Claims (2)

In the skin material that covers the vehicle seat that contains a member such as an acoustic device or a ventilation device,
The said skin material is the structure which covers the facing location of the said member with the leather provided with a silver surface layer and a fiber layer, and the said leather coat | covers the through-hole formed in at least one part of the said facing location, and the said fiber layer. Equipped with a resin layer,
The resin layer has a first part facing the member and a second part formed around the first part, and the second part is configured with a smaller amount of resin than the first part. A skin material for a vehicle seat that is configured to have a flexibility that can be deformed corresponding to the outer shape of the vehicle seat. 2. The vehicle seat according to claim 1, wherein the resin layer is formed with regularity in which the amount of the resin decreases continuously or stepwise from the first part toward the second part. Skin material.

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