JP7587773B2 - Ceiling covering material - Google Patents

Description

The present invention relates to a covering material for automobile ceilings.

Conventionally, in automobile ceiling materials, a laminated material in which a skin material with texture and design is used on the front side and a cushioning material such as soft polyurethane foam is laminated on the back side is adhered to the automobile ceiling base material. For example, a vehicle seat interior material is disclosed in which a knitted fabric, nonwoven fabric, suede-like synthetic leather, etc. is used as a skin material, polyurethane foam is laminated on the back side, and a vehicle seat interior material is laminated via an adhesive layer to form the material (Patent Document 1).

However, vehicle seat interior materials, in which the skin material and polyurethane foam are laminated, have the problem that recycling the material is difficult because it is a composite material of different materials. In addition, polyurethane foam containing flame retardants is used to meet the flame retardancy standards for interior materials used in automobiles, which increases material costs, and the labor and time required to laminate it on the back side of the skin material increases manufacturing costs.

The applicant then discovered that by raising the reverse side of a tricot knit fabric as a skin material and making it to a specific thickness, cushioning properties are imparted and it is possible to omit the use of soft polyurethane foam. He then filed an invention for an interior skin material for vehicles, such as automobiles, in which the reverse side of the skin material is raised and the material is bonded directly to the base layer without an intermediate urethane layer, eliminating the bonding process for the soft polyurethane foam, improving recyclability, and achieving weight reduction, all with a design (Patent Document 2).

Although it was an excellent vehicle interior skin material that was lightweight, had good design and cushioning properties, and could be made more recyclable, the thickness provided by the nap left room for improvement in terms of its ability to recover from stress during use.

JP 2003-245969 A JP 2009-214589 A

The present invention was made in light of this technical background, and its purpose is to provide a ceiling covering material that is flexible and easy to work with in post-processing because it achieves thickness not by raising the fabric, but by using a knitting structure and yarns, eliminating the need to layer polyurethane foam.

To achieve the above objective, the present invention provides the following means:

[1] A skin material to be laminated on a ceiling substrate of an automobile,
The skin material is a tricot knitted fabric knitted by L1 (rear reed), L2 (middle reed) and L3 (front reed) of a tricot knitting machine,
The surface of the needle loop formed by the L1 (rear guide) and the L2 (middle guide) is the surface of the skin material,
The L3 (front reed) has a false twist textured yarn passing through it and has a knitting structure of 2 to 12 needles.
The surface of the skin material where the false twist textured yarn stands in the thickness direction of the skin material is the back surface of the skin material, and the back surface is not raised,
The thickness of the sinker loop is 0.8 mm to 1.6 mm, and the percentage of the thickness (mm) of the skin material is 62% to 76%, and the thickness of the skin material is 1.3 mm to 2.1 mm ;
The bending resistance (bending length) of the skin material in the lateral direction is 64 mm to 95 mm,
The skin material for ceilings is characterized in that one resin selected from the group consisting of polyurethane resin, acrylic resin, and polyester resin is adhered to the skin material.

[2] The ceiling covering material according to paragraph 1 above, in which the false twist textured yarn has a total fineness of 20 dtex to 330 dtex and a single yarn fineness of 0.1 dtex to 22 dtex.

[3] The covering material for ceilings according to the above item 1 or 2, wherein the relationship between the vertical density of the product and the vertical density at the time of knitting in the covering material is expressed by the following formula:
Vertical density ratio: vertical density of product/vertical density during knitting=1.28 to 1.3 6 .

In the invention of [1], the thickness is obtained by the knitting structure and the use of yarns, not by the thickness imparted by raising, and furthermore, since the thickness of the covering material is 1.3 mm to 2.1 mm , it is possible to provide a ceiling covering material that is excellent in flexibility and workability in post-processing, and does not require lamination of polyurethane foam. In addition, since it is not a composite material such as lamination of polyurethane foam, it is possible to provide a ceiling covering material that exhibits high recyclability and realizes reduction in manufacturing costs.

In the invention of [2], the total fineness of the false twisted yarn is 20 dtex to 330 dtex, and the single yarn fineness is 0.1 dtex to 22 dtex, so that the thickness of the ceiling covering material can be ensured by increasing the sinker loop density through the crimping of the false twisted yarn and the shrinkage of the yarn during dyeing.

In the invention [1] , since the lateral bending resistance (bending length) of the covering material is 64 mm to 95 mm , it is possible to improve workability such as handling in the cutting process, molding process, etc. of the ceiling covering material.

In the invention of [1] , the thickness of the sinker loop is 0.8 mm to 1.6 mm , and the percentage of the thickness (mm) of the covering material is 62% to 76% , so that the thickness due to the crimp of the false twist textured yarn used in the sinker loop and the shrinkage of the yarn can be ensured, and a flexible ceiling covering material can be obtained. The jump of the yarn due to the underlap knitted at L3 (front reed) forms a loop due to the shrinkage of the knitted fabric in the dyeing process, and this loop absorbs the unevenness of the ceiling base material and exhibits flexibility so that a flat finish can be obtained on the surface of the covering material.

In the invention [1] , one resin selected from the group consisting of polyurethane resin, acrylic resin, and polyester resin is adhered to the tricot knit fabric, so that the ceiling covering material can be provided with appropriate stiffness.

1 is a schematic cross-sectional view showing one embodiment of a ceiling covering material according to the present invention. FIG. 2 is an explanatory diagram showing the joining of the ceiling covering material shown in FIG. 1 to a ceiling base material. FIG. 1 is an explanatory diagram showing an example of a skin layer according to a conventional technique. 1 shows the knit structure of the tricot knit fabric of Example 1.

Next, one embodiment of the vehicle interior material according to the present invention will be described with reference to the drawings.

A ceiling covering material 1 according to the present invention is a covering material laminated on a ceiling base material 4 of an automobile, the covering material being a tricot knitted fabric knitted by L1 (rear reed), L2 (middle reed) and L3 (front reed) of a tricot knitting machine, the surface of needle loops 2 formed by L1 (rear reed) and L2 (middle reed) being the front surface of the covering material, a false twist textured yarn being passed through L3 (front reed) to form a knitted structure of 2 to 12 needle swings, the surface of sinker loops 3 on which the false twist textured yarn stands in the thickness direction of the covering material being the back surface of the covering material, the back surface being not raised, the thickness of the sinker loops being 0.8 mm to 1.6 mm, the percentage of the thickness (mm) of the covering material being 62% to 76%, and the thickness of the covering material being 1.3 mm to 2.1 mm,
The bending resistance (bending length) of the skin material in the lateral direction is 64 mm to 95 mm,
The skin material is characterized in that one resin selected from the group consisting of polyurethane resin, acrylic resin, and polyester resin is adhered to the skin material .

By adopting this type of configuration, thickness can be achieved through the knitting structure and use of yarn, rather than through the raising process, making it possible to provide a ceiling covering material 1 that does not require laminating polyurethane foam 5-2.

Examples of fibers constituting the skin material of the present invention include synthetic fibers such as polyester fibers, polyurethane fibers, and polypropylene fibers. These may be combined as appropriate. Among these, those containing polyester fibers are preferred from the viewpoint of maintaining excellent weather resistance for automobile use.

The tricot fabric of the present invention is knitted by L1 (rear reed), L2 (middle reed) and L3 (front reed) of a tricot knitting machine having three or more reeds, the yarn of L2 (middle reed) connects the yarn of L3 (front reed) and the yarn of L1 (rear reed) to form needle loops 2, and the false twist textured yarn of L3 (front reed) forms sinker loops 3 by a knitting structure of 2 to 12 needle swings. The tricot fabric knitted in this way has a surface on which the needle loops 2 are formed, a small pattern with no directionality, and a plain appearance. On the other hand, the surface of the sinker loops 3 where the false twist textured yarn stands in the thickness direction of the skin material is the back surface of the ceiling skin material 1, and the thickness of the skin material is 1.3 mm to 2.1 mm . In the present invention, the tricot fabric is knitted using L1 (rear reed), L2 (middle reed), and L3 (front reed) of a tricot knitting machine, and a three-reed fabric is used in which the needle loop surfaces of L1 (rear reed) and L2 (middle reed) form the surface of the skin material. However, depending on needs, a four-reed fabric in which a knitting pattern is knitted using L3 (middle front reed) and L4 (front reed), L2 (middle reed) forms the ground structure, L1 (rear reed) has a cord knitting structure, and the sinker loop surfaces form the surface of the skin material may be used as the ceiling skin material.

The back side of the ceiling covering material 1 is laminated facing the ceiling base material 4 and then adhesively molded according to the shape of the ceiling. By placing the needle loop 2 face on the front side and the sinker loop 3 face on the back side during adhesive molding, the unevenness of the ceiling base material 4 is absorbed, resulting in a smooth finish that maintains the quality of the ceiling surface.

The false twisted yarn of L3 (front reed) forms sinker loops 3 with a knitting structure of 2 to 12 needles, but with a Denbi knitting structure with less than 2 needles, the yarn length of the sinker loops 3 is short, making it difficult to obtain the thickness required for ceilings that do not require polyurethane foam. Conversely, with a knitting structure with more than 12 needles, the weft stretch of the knitted fabric decreases, making it easier for wrinkles to occur when the ceiling covering material 1 is formed.

There are no particular restrictions on the gauge of the tricot knitting machine, but it is preferable to use a knitting machine with a gauge of 22 to 36/inch. If it is less than 22/inch, the knitting density will be coarse and the adhesive used to bond the ceiling base material 4 to the covering material may easily seep out, which is not preferable. Conversely, if it exceeds 36/inch, it will be difficult to knit with thick yarn, and there is a risk that the thickness will not be maintained, which is not preferable.

In addition, the number of courses on the knitting machine during tricot knitting is preferably 35 to 65 courses per inch. Less than 35 courses per inch is not preferred because the knit density is coarse and the resin used to bond the ceiling base material 4 to the covering material may easily seep out. Conversely, if it exceeds 65 courses per inch, it is not preferred because the stretchability of the knit decreases and wrinkles may easily occur when the ceiling covering material is molded.

In the present invention, the thickness of the skin material is obtained by the knitting structure and the use of yarn, and the thickness is 1.3 mm to 2.1 mm . More specifically, by increasing the runner length of the false twist textured yarn of L3 (front reed), the false twist textured yarn forms a loop standing in the thickness direction of the skin material, thereby imparting thickness.

The runner length is preferably 220 cm or more. More preferably, it is in the range of 280 cm to 600 cm. If the runner length is less than 220 cm, the knitted fabric will be thin, which is undesirable because there is a risk that the resin used to bond the ceiling base material 4 to the covering material will seep out or that the unevenness of the ceiling base material 4 will not be fully absorbed. Conversely, if it exceeds 600 cm, the knitted fabric will be thick, which is undesirable because there is a risk that the knitted fabric will be packed in during the dyeing process and wrinkles will easily occur.

Furthermore, the thickness of the sinker loop 3 is in the range of 0.8 mm to 1.6 mm , and the percentage of the thickness (mm) of the skin material is in the range of 62% to 76% . If the thickness of the sinker loop 3 is less than 0.4 mm, the knitted fabric becomes thin, which is undesirable because there is a risk that the resin used to bond the ceiling base material 4 and the skin material will seep out or that the unevenness of the ceiling base material 4 will not be absorbed. Conversely, if the thickness exceeds 2.0 mm, the knitted fabric becomes thick, which is undesirable because there is a risk that the knitted fabric will be packed in and wrinkled during dyeing.

In addition, if the percentage of the sinker loops 3 in the thickness (mm) of the skin material is less than 40%, the knitted fabric will be thin, which is undesirable because there is a risk that the resin used to bond the ceiling base material 4 to the skin material will seep out or that the unevenness of the ceiling base material 4 will not be fully absorbed. Conversely, if it exceeds 80%, the knitted fabric will be thick, which is undesirable because there is a risk that the knitted fabric will be packed in during dyeing and wrinkles will easily occur.

The false twisted yarn is a yarn that has been temporarily twisted using a known method, heated, and then untwisted, resulting in a fluffy, soft texture and bulky yarn.

It is preferable that the total fineness of the false twisted yarn is in the range of 20 dtex to 330 dtex, and the single yarn fineness is in the range of 0.1 dtex to 22 dtex. More preferably, the single yarn fineness is in the range of 1 dtex to 5 dtex. If the total fineness is less than 20 dtex, the knitted fabric will be thin, which is undesirable because there is a risk that the resin used to bond the ceiling base material 4 and the covering material will seep out and that the unevenness of the ceiling base material 4 will not be fully absorbed. Conversely, if the total fineness exceeds 330 dtex, the knitted fabric will be thick, which is undesirable because there is a risk that the knitted fabric will be packed in and wrinkled during dyeing. At the same time, if the single yarn fineness is less than 0.1 dtex, the knitted fabric may deform when a load is applied to the surface of the skin material, making it difficult to maintain the thickness of the knitted fabric. Conversely, if the single yarn fineness exceeds 22 dtex, the yarn becomes stiff and may protrude onto the surface of the needle loop 2 during knitting, resulting in a poor tactile feel, which is undesirable.

The horizontal bending resistance (bending length) of the covering material of the present invention is in the range of 64 mm to 95 mm . If the horizontal bending resistance (bending length) is less than 35 mm, it is too soft and the ceiling covering material may be difficult to handle (i.e., workability may be poor) during molding, which is not preferred. Conversely, if it exceeds 110 mm, it is not preferred because the ceiling covering material may be prone to folding and wrinkling.

Moreover, one resin selected from the group consisting of polyurethane resin, acrylic resin, and polyester resin is attached to the tricot knit fabric . This resin is preferred because it has good affinity with the resin used for the adhesion.

To laminate the ceiling skin material 1 of the present invention to the ceiling base material 4 of an automobile, a method of pressing and laminating using resin can be used, either simultaneously with molding or after molding, to match the shape of the ceiling.

The surface of the sinker loop 3 may be raised, as this is expected to provide an anchoring effect during adhesion. In this case, the raising is for the purpose of providing an anchoring effect rather than increasing thickness, so loop or semi-cut raising is preferred, and the method of raising the nap is not particularly limited, but examples include raising with needle cloth and sandpaper. When raising the nap, it is a good idea to apply a raising oil agent beforehand.

Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples. In the examples and comparative examples, polyester fiber is used as the knitting yarn, and Table 1 shows the yarn count, knitting structure, and runner length used. In the knitting yarn column, T stands for dtex, and SD stands for semi-dull. Table 2 shows the evaluation results.

Example 1
A 3-reed tricot knitting machine with a gauge of 28 was used to knit the knitted fabric as shown in FIG. 4. That is, polyester 56 dtex/24f FDY (full draw yarn) semi-dull yarn was introduced in 1-in-1-out to L1 (rear reed) and L2 (middle reed), respectively, and polyester 110 dtex/48f DTY (drone textured yarn) semi-dull yarn was introduced in full set to L3 (front reed), and the cord knitted fabric was knitted so that it had 6 underlap needles. The runner lengths of L3 to L1 were as shown in Table 1. Next, the obtained knitted fabric was dyed with a disperse dye at a temperature of 135°C for 15 minutes using a liquid flow dyeing machine, and then dehydrated, spread, and dried at a temperature of 150°C for 2 minutes. Next, the dried knitted fabric was dipped in a polyester resin dispersion (resin concentration 6%) to apply polyester resin to the entire knitted fabric. The sheet was then subjected to a tentering process at 160°C for 2 minutes to obtain a ceiling covering material. The resulting ceiling covering material had a basis weight of 280 g/ ^m2 , a density of 38 wales/inch, and 45 courses/inch. The total thickness was 1.3 mm, the sinker loop thickness was 0.8 mm, the ratio (%) of the loop thickness to the total thickness was 62%, and the transverse bending resistance (bending length) was 64 mm. Therefore, the thickness, flexibility, and workability were all evaluated as "A", passing the test.

<Reference Example 1>
In Example 1, a ceiling covering material was obtained in the same manner as in Example 1, except that polyester 110 dtex/48 fDTY (drone textured yarn) semi-dull yarn was introduced in a full set for L3 (front reed), the cord knitting structure was made to have three underlap needles, and the knitting structure of L3 and the runner lengths of L3 to L1 were as shown in Table 1. The resulting ceiling covering material had a basis weight of 220 g/ ^m2 , a density of 38 wales/inch, and 45 courses/inch. In addition, the total thickness was 1.0 mm, the thickness of the sinker loop was 0.5 mm, the ratio (%) of the loop thickness to the total thickness was 50%, and the bending resistance (bending length) in the weft was 41 mm. Therefore, the evaluation of thickness, flexibility, and workability were all "good", and the material was passed.

<Reference Example 2>
A ceiling covering material was obtained in the same manner as in Example 1, except that the knitting yarn in Example 1 was replaced with the knitting yarn shown in Table 1, the runner lengths L3 to L1 were as shown in Table 1, and the knitted fabric was not dipped in a polyester resin dispersion (resin concentration 6%). The resulting ceiling covering material had a basis weight of 320 g/ ^m2 , a density of 3.8 wales/inch, and 41 courses/inch. The total thickness was 1.5 mm, the sinker loop thickness was 0.9 mm, the ratio (%) of the loop thickness to the total thickness was 60%, and the weft stiffness (bending length) was 45 mm. Thus, the thickness and flexibility were both rated as "◎", and the workability was rated as "◯", so all were acceptable.

<Reference Example 3>
A ceiling covering material was obtained in the same manner as in Reference Example 2 , except that a semi-cut raising process was performed on the surface of the sinker loop of the knitted fabric to a raising thickness of 0.4 mm using a raising machine. The resulting ceiling covering material had a basis weight of 338 g/m2, a density of 39 wales/inch, and 40 courses/inch. The total thickness was 1.8 mm, the sinker loop thickness was 1.3 mm, the ratio (%) of the loop thickness to the total thickness was 72%, and the weft stiffness (bending length) was 58 mm. Therefore, the evaluations of thickness, flexibility, and workability were all evaluated as "A", passing the evaluation.

<Reference Example 4>
In Example 1, the 28-gauge knitting machine was replaced with a 36-gauge three-reed tricot knitting machine, the knitting yarn of L3 (front reed) was replaced with polyester 84 dtex/36 fDTY (drone textured yarn) semi-dull yarn, which was introduced in a full set, the cord knitting structure had 8 underlap needles, the knitting structure of L3 and the runner lengths of L3 to L1 were as shown in Table 1, and the knitted fabric was not dipped in polyester resin dispersion (resin concentration 6%). The ceiling covering material was obtained in the same manner as in Example 1. The basis weight of the obtained ceiling covering material was 340 g/m2, the density was 48 wales/inch, and 57 courses/inch. In addition, the total thickness was 1.6 mm, the thickness of the sinker loop was 1.0 mm, the ratio (%) of the loop thickness to the total thickness was 63%, and the bending resistance (bending length) in the weft was 48 mm. Therefore, the thickness and flexibility were both rated as "A", and the workability was rated as "◯", so all were acceptable.

Example 2
In Reference Example 4 , a full set of polyester 84 dtex/36 fDTY (drone textured yarn) semi-dull yarn was introduced into L3 (front reed), the cord knitting structure had 12 underlap needles, the knitting structure of L3 and the runner lengths of L3 to L1 were as shown in Table 1, and the knitting fabric was dipped in a polyester resin dispersion (resin concentration 6%). Except for this, a ceiling covering material was obtained in the same manner as in Reference Example 4. The basis weight of the obtained ceiling covering material was 400 g/ ^m2 , the density was 46 wales/inch, and 53 courses/inch. In addition, the total thickness was 2.1 mm, the thickness of the sinker loop was 1.6 mm, the ratio (%) of the loop thickness to the total thickness was 76%, and the bending resistance (bending length) in the weft was 95 mm. Therefore, the evaluation of thickness, the evaluation of flexibility, and the evaluation of workability were all "◎", and all were passed.

<Comparative Example 1>
In Reference Example 1 , the knitting yarn was replaced with the knitting yarn shown in Table 1, and the runner lengths of L3 to L1 were set as shown in Table 1. The fabric was not dipped in a polyester resin dispersion (resin concentration 6%), and the same procedure was followed to obtain a skin material. The obtained skin material had a basis weight of 180 g/ ^m2 , a density of 46 wales/inch, and 53 courses/inch. The total thickness was 0.7 mm, the thickness of the sinker loop was 1.4 mm, the ratio (%) of the loop thickness to the total thickness was 49%, and the bending resistance (bending length) in the horizontal direction was 28 mm. Therefore, the evaluation of thickness and workability were both "x", and only the evaluation of flexibility was "◯", which was a pass. Thus, it was inappropriate as a skin material for ceilings in automobiles that do not require polyurethane foam.

The ceiling covering material obtained as described above was evaluated according to the following evaluation methods.

<Thickness evaluation method>
The cross section of the skin material in the width direction was observed using a microscope (Keyence Corporation, Digital Microscope VHX-6000) and the total thickness of the skin material was measured. Evaluation was performed according to the following criteria, with a rating of "◯" or higher being considered a pass.
(Judgment criteria)
"◎": 1.2 mm or more "〇": 0.9 mm or more and less than 1.2 mm "×": Less than 0.9 mm

<How to evaluate flexibility>
The flexibility that can absorb the unevenness of the ceiling base material 4 and obtain a flat and smooth finish that maintains the quality of the surface of the skin material was evaluated from the ratio of the sinker loop thickness. Specifically, the thickness of the sinker loop of the skin material was observed using a microscope (Keyence Corporation, Digital Microscope VHX-6000), and the loop thickness was measured and the ratio to the total thickness was calculated. Evaluation was performed according to the following criteria, and a rating of "◯" or higher was considered to be a pass.
(Judgment criteria)
"◎": 60% or more but less than 80% "〇": 40% or more but less than 60% "×": Less than 40%

<Method for evaluating workability>
When bonding the covering material and the ceiling base material, the degree of wrinkles on the covering material varies depending on the stiffness of the knitted fabric, so the work time tends to increase because the work is performed while removing the wrinkles or preventing the wrinkles from occurring. Therefore, since the workability is improved when the wrinkles are suppressed, the workability was evaluated from the stiffness. The stiffness (bending length) was measured in accordance with the 45° cantilever method of JIS L 1096 (2010 edition). The test pieces were cut to a size of 2.5 cm wide x 20 cm long, with the wale direction of the knitted fabric as the horizontal direction and the course direction of the knitted fabric as the vertical direction. The test piece was gently pushed out from a smooth flat table with a 45° slope onto the slope, and the length of the test piece pushed out when the end contacted the slope was taken as the stiffness. Evaluation was performed according to the following criteria, and a rating of "◯" or higher was considered to be a pass.
(Judgment criteria)
"◎": 50mm or more and less than 110mm "〇": 35mm or more and less than 50mm "×": Less than 35mm

As is clear from Table 2, the ceiling covering materials of Examples 1 and 2 according to the present invention were excellent in flexibility due to the thickness achieved by the knitting structure and use of yarns, and were covering materials that did not require lamination of polyurethane foam because of their excellent workability in post-processing. In contrast, the fabric of Comparative Example 1 was flexible but had significantly poor thickness and workability, rated "x".

The ceiling covering material of the present invention does not require lamination of polyurethane foam and has excellent flexibility, making it suitable for use as a ceiling covering material.

1...Skin material (skin material for ceiling)
2: Needle loop 3: Sinker loop 4: Ceiling base material 5: Skin layer 5-1: Skin 5-2: Polyurethane foam (soft)
T: Thickness of the skin
T1: Thickness of the sinker loop

Claims (3)

A skin material to be laminated on a ceiling base material of an automobile,
The skin material is a tricot knitted fabric knitted by L1 (rear reed), L2 (middle reed) and L3 (front reed) of a tricot knitting machine,
The surface of the needle loop formed by the L1 (rear guide) and the L2 (middle guide) is the surface of the skin material,
The L3 (front reed) has a false twist textured yarn passing through it and has a knitting structure of 2 to 12 needles.
The surface of the skin material where the false twist textured yarn stands in the thickness direction of the skin material is the back surface of the skin material, and the back surface is not raised,
The thickness of the sinker loop is 0.8 mm to 1.6 mm, and the percentage of the thickness (mm) of the skin material is 62% to 76%, and the thickness of the skin material is 1.3 mm to 2.1 mm ;
The bending resistance (bending length) of the skin material in the lateral direction is 64 mm to 95 mm,
The skin material for ceilings is characterized in that one resin selected from the group consisting of polyurethane resin, acrylic resin, and polyester resin is adhered to the skin material . The ceiling covering material according to claim 1, wherein the false twist textured yarn has a total fineness of 20 dtex to 330 dtex and a single yarn fineness of 0.1 dtex to 2.2 dtex. 3. The ceiling covering material according to claim 1, wherein the relationship between the vertical density of the product and the vertical density at the time of knitting is expressed by the following formula:
Vertical density ratio: Vertical density of product / Vertical density during knitting = 1.28 to 1.3 6

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